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.util.*;
import java.util.concurrent.LinkedBlockingDeque;
import java.io.*;
import java.lang.*;
	
	public class graph1
	{
		public static int n;
		public static ArrayList<Integer> adj[];
		public static ArrayList<Integer> lev[];
		
		public static boolean[] vis;
		public static int[] par;
		public static boolean[] ans;
		public static int[] level;
		public static int count;
		
		public static long INF = Long.MAX_VALUE/100;
		
		public static int[] ta;
		public static int[] tb;
		public static int[] t;
		
		
		public static HashSet<pair> prob;
		
		public static void main(String[] args)
		{
			InputReader in = new InputReader(System.in);
			PrintWriter pw = new PrintWriter(System.out);
	
			n = in.nextInt();
			int x = in.nextInt();
			vis = new boolean[n+1];
			ans = new boolean[n+1];
			
			par = new int[n+1];
			level = new int[n+1];
			
			ta = new int[n+1];
			tb = new int[n+1];
			t = new int[n+1];
			
			
			adj = new ArrayList[n+1];
			for(int i=0; i<=n; i++)
				adj[i] = new ArrayList<>();
			
			
			for(int i=0; i<n-1; i++)
			{
				int u = in.nextInt();
				int v = in.nextInt();
				adj[u].add(v);
				adj[v].add(u);
			
			}
			
			bfs(1);
			
			vis = new boolean[n+1];	
			fun(x);
			
			int max = 0;
			for(int i=1; i<=n; i++)
			{
				//pw.print(t[i]+" ");
				max = Math.max(max, t[i]);
			}
			pw.println(max);
			
			
			
			//code ends....
			pw.flush();
			pw.close();
		}
		
		
	
		
		
		public static void bfs(int x)
		{
			Queue<Integer> queue = new LinkedList<>();
			queue.add(x);
			vis[x] = true;
			
			while(!queue.isEmpty())
			{
				int last = queue.poll();
				for(int p : adj[last])
				{
					if(!vis[p])
					{
						queue.add(p);
						ta[p] = ta[last]+1;
						vis[p] = true;
					}
				}
			}
		}
		

		public static void fun(int x)
		{
			Queue<Integer> queue = new LinkedList<>();
			queue.add(x);
			vis[x] = true;
			tb[x] = 0;
			t[x] = 2*ta[x];
			//ans[1] = true;
			while(!queue.isEmpty())
			{
				int last = queue.poll();
				for(int p : adj[last])
				{
					if(!vis[p])
					{
						queue.add(p);
						tb[p] = tb[last]+1;
						if(ans[last])
							ans[p] = true;
					//	System.out.println(p+" "+ta[p]+" "+tb[p]+" "+ans[last]);
						if(!ans[p])
						{
							t[p] = 2*Math.max(ta[p], tb[p]);
							if(ta[p]<tb[p])
									t[p]--;
							
									
							count = Math.max(count, 2*Math.max(ta[p], tb[p]));
						
						}
						if(ta[p]<=tb[p])
							ans[p] = true;
						
						vis[p] = true;
					}
				}
			}
		}
		
		

	
		
		
		
		
		
		public static int fbfs(int x)
		{
			Queue<Integer> queue = new LinkedList<>();
			queue.add(x);
			int c = 0;
			vis[x] = true;
			while(!queue.isEmpty())
			{
				int last = queue.poll();
				for(int p : adj[last])
				{
					if(!vis[p])
					{
						queue.add(p);
						vis[p] = true;
						c++;
						par[p] = last;
					}
				}
			}
			return c;
		}
		
		
		
		
		public static void dfsrec(int s, int l)
		{
			if(vis[s])
				return;
			
			vis[s] = true;
			int k = 0;
			//System.out.println(s);
			for(int p: adj[s])
			{
				boolean f2 = false;
				if(!vis[p])
				{
					par[p] = s;
					///System.out.println(p+" "+s);
					dfsrec(p, l+1);
				}
				
			}
			count = Math.max(l, count);
		}
		
		
		/*
		
		
		public static void fun(int s)
		{
			
			if(vis[s])
				return;
			set[s] = count;
			vis[s] = true;
			fun(a[s]);
			
		}
		

		public static int dfs(int s)
		{
			for(int i=0; i<=n; i++)
			{
				vis [i] = false;
				par[i] = -1;
				level[i] = 0;
				
			}
			Stack<Integer> stk = new Stack<>();
	 		stk.add(s);
			par[s] = 0;
			vis[s] = true;
			
			while(!stk.isEmpty())
			{
				int last = stk.pop();
			///	System.out.println(last);
				boolean f = false;
				for(int a : adj[last])
				{
					if(!vis[a])
					{
						//child[last].add(a);
						stk.add(a);
						par[a] = last;
						level[a] = level[last] +1;
						vis[a] = true;
					}
				}
			
			}
			int max = 0;
			int maxi = 0;
			for(int i=1; i<=n; i++)
			{
				if(level[i]>max)
				{
					max = level[i];
					maxi = i;
				}
				
			}
			return maxi;
		}
				
		 */
	
		
/*		
		
		public static int find(int i) {
			
			
			if(par[i]==-1)
				return i;
			else
				return find(par[i]);
				
		}
		
		 public static void union( int x, int y)
		    {
		        int xset = find( x);
		        int yset = find(y);
		        par[xset] = yset;
		    }

	 */
		
		
	/*	 public static boolean cycle(HashSet<pair> set) {
			 
			 
			 for(pair p: set)
			 {
				 int x = find(p.x);
				 int y = find(p.y);
				 if(x==y)
					 return true;
		
				 union(x, y);
				 
			 }
			 
			 return false;
		 }
		 */
		
		
		
		
		
		
		static class pair implements Comparable<pair>
		 
		{
			Long x;
			Integer y;
			pair(long adj,int y)
			{
		
				this.x=adj;
				this.y=y;
			}
			
			public int compareTo(pair o) {
				//int result = x.compareTo(o.x);
				//if(result==0)
					int result = -y.compareTo(o.y);
				
				return result;
			}  
			
			public String toString()
			{
				return x+" "+y;
			}
			
			public boolean equals(Object o)
			{
				if (o instanceof pair)
			    {
					pair p = (pair)o;
					return p.x == x && p.y == y ;
				}
				return false;
			}
			
			public int hashCode()
			{
				return new Long(x).hashCode()*31 + new Long(y).hashCode();
			}
		}
	
	
		static class triplet implements Comparable<triplet>
		{
			Integer x,y,z;
			triplet(int x,int y,int z)
			{
				this.x = x;
				this.y = y;
				this.z = z;
			}
			
			public  int compareTo(triplet o)
			{
				int result = x.compareTo(o.x);
				if(result==0)
					result =  y.compareTo(o.y);
				if(result==0)
					result = z.compareTo(o.z);
	
				return result;
			}
			
			public boolean equlas(Object o)
			{
				if(o instanceof triplet)
				{
					triplet p = (triplet)o;
					return x==p.x && y==p.y && z==p.z;
				}
				return false;
			}
			
			public String toString()
			{
				return x+" "+y+" "+z;
			}
			public int hashCode()
			{
				return new Long(x).hashCode()*31 + new Long(y).hashCode() + new Long(z).hashCode(); 
			}
		}
		
	
		
		
		
		static class InputReader 
		{
			 
			private final InputStream stream;
			private final 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 String nextLine() 
			{
				int c = snext();
				while (isSpaceChar(c))
					c = snext();
				StringBuilder res = new StringBuilder();
				do 
				{
					res.appendCodePoint(c);
					c = snext();
				} while (!isEndOfLine(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;
			}
	 
			private boolean isEndOfLine(int c) 
			{
				return c == '\n' || c == '\r' || c == -1;
			}
	 
			public interface SpaceCharFilter
		    {
				public boolean isSpaceChar(int ch);
			}
		}
		
		public static long mod = 1000000007;
		public static int d;
		public static int p;
		public static int q;
		
		public static int[] suffle(int[] a,Random gen)
		{
			int n = a.length;
			for(int i=0;i<n;i++)
			{
				int ind = gen.nextInt(n-i)+i;
				int temp = a[ind];
				a[ind] = a[i];
				a[i] = temp;
			}
			return a;
		}
		
		public static void swap(int a, int b){
			int temp = a;
			a = b;
			b = temp;
		}
		
		public static HashSet<Integer> primeFactorization(int n)
		{
			HashSet<Integer> a =new HashSet<Integer>();
			for(int i=2;i*i<=n;i++)
			{
				while(n%i==0)
				{
					a.add(i);
					n/=i;
				}
			}
			if(n!=1)
				a.add(n);
			return a;
		}
		
		public static void sieve(boolean[] isPrime,int n)
		{
			for(int i=1;i<n;i++)
				isPrime[i] = true;
			
			isPrime[0] = false;
			isPrime[1] = false;
			
			for(int i=2;i*i<n;i++)
			{
				if(isPrime[i] == true)
				{
					for(int j=(2*i);j<n;j+=i)
						isPrime[j] = false;
				}
			}
		}
		
		public static int GCD(int a,int b)
		{
			if(b==0)
				return a;
			else
				return GCD(b,a%b);
		}
		
		public static long GCD(long a,long b)
		{
			if(b==0)
				return a;
			else
				return GCD(b,a%b);
		}
		
		public static void extendedEuclid(int A,int B)
		{
			if(B==0)
			{
				d = A;
				p = 1 ;
				q = 0;
			}
			else
			{
				extendedEuclid(B, A%B);
				int temp = p;
				p = q;
				q = temp - (A/B)*q;
			}
		}
		
		public static long LCM(long a,long b)
		{
			return (a*b)/GCD(a,b);
		}
		
		public static int LCM(int a,int b)
		{
			return (a*b)/GCD(a,b);
		}
		
		public static int binaryExponentiation(int x,int n)
		{
		    int result=1;
		    while(n>0)
		    {
		        if(n % 2 ==1)
		            result=result * x;
		        x=x*x;
		        n=n/2;
		    }
		    return result;
		}
		
		public static long binaryExponentiation(long x,long n)
		{
		    long result=1;
		    while(n>0)
		    {
		        if(n % 2 ==1)
		            result=result * x;
		        x=x*x;
		        n=n/2;
		    }
		    return result;
		}
		
		public static int modularExponentiation(int x,int n,int M)
		{
		    int result=1;
		    while(n>0)
		    {
		        if(n % 2 ==1)
		            result=(result * x)%M;
		        x=(x*x)%M;
		        n=n/2;
		    }
		    return result;
		}
		
		public static long modularExponentiation(long x,long n,long M)
		{
		    long result=1;
		    while(n>0)
		    {
		        if(n % 2 ==1)
		            result=(result * x)%M;
		        x=(x*x)%M;
		        n=n/2;
		    }
		    return result;
		}
		
		public static int modInverse(int A,int M)
		{
		    return modularExponentiation(A,M-2,M);
		}
		
		public static long modInverse(long A,long M)
		{
		    return modularExponentiation(A,M-2,M);
		}
		
		
		
		
		
		public static boolean isPrime(int n)
		{
		    
		    if (n <= 1)  return false;
		    if (n <= 3)  return true;
		    
		    if (n%2 == 0 || n%3 == 0) 
		    	return false;
		 
		    for (int i=5; i*i<=n; i=i+6)
		    {
		        if (n%i == 0 || n%(i+2) == 0)
		           return false;
		    }
		    
		    return true;
		}
		
		
	}