Alice got tired of playing the tag game by the usual rules so she offered Bob a little modification to it. Now the game should be played on an undirected rooted tree of n vertices. Vertex 1 is the root of the tree.

Alice starts at vertex 1 and Bob starts at vertex x (x ≠ 1). The moves are made in turns, Bob goes first. In one move one can either stay at the current vertex or travel to the neighbouring one.

The game ends when Alice goes to the same vertex where Bob is standing. Alice wants to minimize the total number of moves and Bob wants to maximize it.

You should write a program which will determine how many moves will the game last.

Input

The first line contains two integer numbers n and x (2 ≤ n ≤ 2·105, 2 ≤ x ≤ n).

Each of the next n - 1 lines contains two integer numbers a and b (1 ≤ a, b ≤ n) — edges of the tree. It is guaranteed that the edges form a valid tree.

Output

Print the total number of moves Alice and Bob will make.

Examples

Input

4 3
1 2
2 3
2 4


Output

4


Input

5 2
1 2
2 3
3 4
2 5


Output

6

Note

In the first example the tree looks like this:

<image>

The red vertex is Alice's starting position, the blue one is Bob's. Bob will make the game run the longest by standing at the vertex 3 during all the game. So here are the moves:

B: stay at vertex 3

A: go to vertex 2

B: stay at vertex 3

A: go to vertex 3

In the second example the tree looks like this:

<image>

The moves in the optimal strategy are:

B: go to vertex 3

A: go to vertex 2

B: go to vertex 4

A: go to vertex 3

B: stay at vertex 4

A: go to vertex 4
import java.io.*;
    import java.math.BigInteger;
import java.text.DecimalFormat;
import java.util.*;
 
 
 
     
     
    public  class Main {
    	public static InputReader in;
        public static PrintWriter pw;
     
     
     
    	public static void main(String args[]) 
    	{
    		new Thread(null, new Runnable() {
                public void run() {
                    try{
                        solve();
                    }
                    catch(Exception e){
                        e.printStackTrace();
                    }
                }
            }, "1", 1 << 26).start();
        }
    	static ArrayList<Integer> g[];
    	static ArrayList<Integer> h[];
    	static boolean visited[];
    	static int[] parent;
    	static int par[];
    	static int degree[];
    	static int edjes=0;
    	static int start=-1;
    	static int end=-1;
    	static int Total=0;
    	static int time1[];
    	static int time2[];
    	static int glob=0;
    	static int[] ans;
    	static boolean vis2[][];
    	//static long sum1=0;
    	//static long val[];
        static ArrayList<Integer> levels[];
        static int max=0;
        static int lev=1;
        static ArrayList<Integer> nodes[];
        static ArrayList<Integer> values[];
        static int depth[];
        static boolean found=false;
       // static long sm[];
        static int sum1=0;
        static int pre[][];
        static int subtree[];
       static  int cnt=0;
       static  HashMap<String,Integer> hm;
       static int sm[];
       static int size[];
       static long mul[];
       static long d[]=new long[1000000];
       static int tot=0;
       static long highest=(long)1e9;
       static boolean bit=false;
        static Stack<Integer> tt=new Stack();
       static HashSet<Character> set;
 	   static long fact[],num[];
 	   static long MOD=1000000007;
 	   static int value[];static int premen[];
 	   static int count=0,index=0;
 	   static double ans11[];
 	   static int price[];
 	   static ArrayList<String> hp[][];
 	   static boolean visit[][];
 	   static int cnu[]=new int[1000001];
 	   static int label=1;
 	   static int his[][];
 	   static int size1=0;
 	   static int up[],down[];
 	   static int TotalUp=0;
 	   static long dist[];
 	//   static HashMap<String,Integer> hm1=new HashMap();
 	  // static HashMap<Integer,Integer> hm2=new HashMap();
 	   static TreeSet<Long> set1=new TreeSet();
 	  static  long DP[][][]=new long[20][200][1500];
 	 	static int t=-1,n=-1;
 	 	static int two[],min[],r[];
 	 	static int total[];static int black[];
 	 	static int Parent[];
 	 	static int max2[];
 	 	static int tin[],tout[],a[];
 	 public static void solve() throws FileNotFoundException{
    		
    	
    		 in = new InputReader(System.in);
    		 pw = new PrintWriter(System.out);  
    	/*	 String p=in.readString();
    	     char c[]=p.toCharArray();
    	     int z[]=new int[p.length()];
    	     z[0]=0;
    	     int left=0;
    	     int right=0;
    	     for(int i=1;i<p.length();i++)
    	     {
    	    	 if(i>right)
    	    	 {
    	    		 
    	    		 left=right=i;
    	    		 while(right<p.length()&&c[right]==c[right-left])
    	    			 right++;
    	    		 z[i]=right-left;
    	    		 right--;
    	    	 }
    	    	 else
    	    	 {
    	    		 int k=i-left;
    	    		 if(z[k]<right-i+1)
    	    		 {
    	    			 z[i]=z[k];
    	    		 }
    	    		 else
    	    		 {
    	    			 left=i;
    	    			 while(right<p.length()&&c[right]==c[right-left])
        	    			 right++;
        	    		 z[i]=right-left;
        	    		 right--;
    	    		 }
    	    	 }
    	    	  
    	     }*/
                int n=in.nextInt();
                int X=in.nextInt();
                g=new ArrayList[n+1];
                for(int i=1;i<=n;i++)g[i]=new ArrayList();
                for(int i=1;i<n;i++)
                {
                	int x=in.nextInt();int y=in.nextInt();
                	g[x].add(y);g[y].add(x);
                 }
                 visited=new boolean[n+1];     
                 depth=new int[n+1];depth[1]=0;
                 depth(1,0);
                 max2=new int[n+1];
                 Arrays.fill(visited,false);
                 Max(1,0);
                 Arrays.fill(visited, false);
                 dist2[X]=0;
                 bfs(X);
                 int ans=0;
                 for(int i=1;i<=n;i++)
                 {
             //   	 System.out.print(max2[i]);
                 }
                 for(int i=1;i<=n;i++)
                 {
                	 
                	 int dist11=depth[i];
                	 int dist22=dist2[i];
                	 if(dist22<dist11)
                	 {
                		 int mx=max2[i];
                		 ans=Math.max(ans,2*mx);
                	 }
                 }
                 System.out.println(ans);
 	 }   
 	 static int dist2[]=new int[1000001];
 	 
 	 public static void bfs(int x)
 	 {
 		 visited[x]=true;
 		 Queue<Integer> Q=new LinkedList<Integer>();
 		 Q.add(x);
 		 while(!Q.isEmpty())
 		 {
 			 int count=Q.size();
 			 while(count>0)
 			 {
 				 int p=Q.poll();
 				 visited[p]=true;
 				 for(int y:g[p])
 				 {
 					 if(!visited[y])
 					 {
 						 dist2[y]=dist2[p]+1;
 						 Q.add(y);
 					 }
 				 }
 				 count--;
 			 }
 		 }
 	 }
 	 public static void Max(int curr,int par)
 	 {
 		 visited[curr]=true;
 		 int trees=0;
 		 for(int x:g[curr])
 		 {
 			 if(!visited[x])
 			 {
 				 trees++;
 				 Max(x,curr);
 				 max2[curr]=Math.max(max2[curr],max2[x]);
 			 }
 		 }
 		 if(trees==0)
 		 {
 			 max2[curr]=depth[curr];
 		 }
 	 }
 	 public static void depth(int curr,int parent)
 	 {
 		 visited[curr]=true;
 		 for(int x:g[curr])
 		 {
 			 if(!visited[x])
 			 {
 				 depth[x]=depth[curr]+1;
 				 depth(x,curr);
 			 }
 		 }
 	 }
 	
 	 static int Par[]=new int[202];
 	 public static void Height(int cur,int par){
 		 Par[cur]=par;
 		 visited[cur]=true;
 		 int t=0;
 		 for(int x:g[cur])
 		 {
 			 if(!visited[x])
 			 { 
 				 t++;
 				 Height(x,cur);
 				 high[cur]=Math.max(high[cur], high[x]+1);
 			 }
 		 }
 		 if(t==0)
 		 {
 			 high[cur]=0;
 		 }
 	
 	 }
 	 static int dia[]=new int[202];
 	 static int high[]=new int[292];
 	 public static void Diameter(int curr,int parent)
 	 {
 		visited[curr]=true;
 		int trees=0;
 		ArrayList<Integer> set=new ArrayList();
 	
 		for(int x:g[curr])
 		{
 			if(!visited[x])
 			{
 				trees++;
 				Diameter(x,curr);
 				dia[curr]=Math.max(dia[curr],high[x]);
 				set.add(high[x]);
 			}
 		}
 		if(set.size()>=2)
 		{
 			Collections.sort(set,Collections.reverseOrder());
 			dia[curr]=Math.max(dia[curr],set.get(0)+set.get(1)+2);
 		}
 		else if(set.size()>0)
 		{
 			dia[curr]=Math.max(dia[curr],set.get(0)+1);
 		}
 		if(trees==0)
 		{
 			dia[curr]=0;
 		}

 	 }
 	 
      	 
 	 public static boolean IsPal(String s)
 	 {
 		 char c[]=s.toCharArray();
 		 for(int i=0;i<c.length/2;i++)
 		 {
 			 if(c[i]!=c[s.length()-1-i])
 				 return false;
 		 }
 		 return true;
 	 }
 	public static void Merge(long[] a,int p,int r){
        if(p<r){
            int q = (p+r)/2;
            Merge(a,p,q);
            Merge(a,q+1,r);
            Merge_Array(a,p,q,r);
        }
    }
    public static void Merge_Array(long a[],int p,int q,int r){
       long b[] = new long[q-p+1];
        long c[] = new long[r-q];
        for(int i=0;i<b.length;i++)
            b[i] = a[p+i];
        for(int i=0;i<c.length;i++)
            c[i] = a[q+i+1];
        int i = 0,j = 0;
        for(int k=p;k<=r;k++){
            if(i==b.length){
                a[k] = c[j];
                j++;
            }
            else if(j==c.length){
                a[k] = b[i];
                i++;
            }
            else if(b[i]<c[j]){
                a[k] = b[i];
                i++;
            }
            else{
                a[k] = c[j];
                j++;
            }
        }
    }
 	 
 	 
 	 
 	
 	
       
 	  public static void dfs1(int curr,int parent)
 	  {
 		  visited[curr]=true;
 		  
 		  for(int x:g[curr])
 		  {
 			  
 			  if(x==parent)continue;
 			  depth[x]=depth[curr]+1;
 			  up[x]=up[curr];
 			  if(h[x].contains(curr)){
 				  up[x]++;
 				  TotalUp++;
 			  }
 			  dfs1(x,curr);
 		  }
 	  }
 	 
        
        
        public static void dfs(int curr,int Parent)
        {
        	visited[curr]=true;
        	size[curr]=1;
        	parent[curr]=Parent;
        	count++;
        	if(value[curr]>0)
        	{
        		index=value[curr];
        	}
        	for(int x:g[curr])
        	{
        		if(!visited[x])
        		{
        			dfs(x,curr);
        			size[curr]+=size[x];
        		}
        	}
        }
        static long ncr(long a, long b){
			if(b>a || b<0) return 0;
			long f = (fact[(int) a]*modInverse(((fact[(int) b]*fact[(int) (a-b)])%MOD), MOD))%MOD;
			return f;
		}
		static long modInverse(long a, long mOD2){
            return  power(a, mOD2-2, mOD2);
}
static long power(long x, long y, long m)
{
    if (y == 0)
        return 1;
    long p = power(x, y/2, m) % m;
    p = (p * p) % m;
 
    return (y%2 == 0)? p : (x * p) % m;
}
 
        public static long gcd(long x, long y) {
    		if (x == 0)
    			return y;
    		else
    			return gcd( y % x,x);
    	}	
        public static long power(long a,long b)
		{
			long result=1;
			while(b>0)
			{
				if(b%2==1)
					result*=a;
				a=a*a;
				b/=2;
			}
			return result;
		}
        static class Pair implements Comparable<Pair>{
        	int val;
        		//HashSet<Integer> s;
        		int index;
        		//int index;
        	//	int h;
        		Pair(int val,int index){
        	     	this.val=val;
        			this.index=index;
        		}
        		@Override
        		public int compareTo(Pair o) {
                          return val-o.val;
        		}
        				
        	}
    	static class InputReader {
     
    		private InputStream stream;
    		private byte[] buf = new byte[8192];
    		private int curChar, snumChars;
    		private SpaceCharFilter filter;
     
    		public InputReader(InputStream stream) {
    			this.stream = stream;
    		}
     
    		public int snext() {
    			if (snumChars == -1)
    				throw new InputMismatchException();
    			if (curChar >= snumChars) {
    				curChar = 0;
    				try {
    					snumChars = stream.read(buf);
    				} catch (IOException e) {
    					throw new InputMismatchException();
    				}
    				if (snumChars <= 0)
    					return -1;
    			}
    			return buf[curChar++];
    		}
     
    		public   int nextInt() {
    			int c = snext();
    			while (isSpaceChar(c))
    				c = snext();
    			int sgn = 1;
    			if (c == '-') {
    				sgn = -1;
    				c = snext();
    			}
    			int res = 0;
    			do {
    				if (c < '0' || c > '9')
    					throw new InputMismatchException();
    				res *= 10;
    				res += c - '0';
    				c = snext();
    			} while (!isSpaceChar(c));
    			return res * sgn;
    		}
     
    		public long nextLong() {
    			int c = snext();
    			while (isSpaceChar(c))
    				c = snext();
    			int sgn = 1;
    			if (c == '-') {
    				sgn = -1;
    				c = snext();
    			}
    			long res = 0;
    			do {
    				if (c < '0' || c > '9')
    					throw new InputMismatchException();
    				res *= 10;
    				res += c - '0';
    				c = snext();
    			} while (!isSpaceChar(c));
    			return res * sgn;
    		}
     
    		public int[] nextIntArray(int n) {
    			int a[] = new int[n];
    			for (int i = 0; i < n; i++)
    				a[i] = nextInt();
    			return a;
    		}
     
    		public String readString() {
    			int c = snext();
    			while (isSpaceChar(c))
    				c = snext();
    			StringBuilder res = new StringBuilder();
    			do {
    				res.appendCodePoint(c);
    				c = snext();
    			} while (!isSpaceChar(c));
    			return res.toString();
    		}
     
    		public boolean isSpaceChar(int c) {
    			if (filter != null)
    				return filter.isSpaceChar(c);
    			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    		}
     
    		public interface SpaceCharFilter {
    			public boolean isSpaceChar(int ch);
    		}
    	}
    }
 