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.*;
import java.nio.file.attribute.AclEntry.Builder;
import java.security.KeyStore.Entry;
import java.util.*;


 public class CODEFORCES {
	private InputStream is;
	private PrintWriter out;
	int time = 0, dp[][], DP[], start[], end[], dist[], red[], black[], MOD = (int)(1e9+7), arr[];
	int MAX = 200000, N, K, L;
	ArrayList<Integer>[] amp;
	boolean b[], boo[][];
	Pair prr[], parent[][];
	HashSet<Integer> hs = new HashSet<>();
	

	public static void main(String[] args) throws Exception {
		new Thread(null, new Runnable() {
		public void run() {
			try {

		//new Main().soln();
		} catch (Exception e) {
				System.out.println(e);
			}
		}
	}, "1", 1 << 26).start();
		new CODEFORCES().soln();
	}
	char ch[][];
	void solve() {
		int n = ni(), x = ni()-1;
		amp = (ArrayList<Integer>[]) new ArrayList[n];
		for(int i = 0; i< n; i++) amp[i] = new ArrayList<>();
		buildGraph(n-1);
		int dist1[] = new int[n];
		int dist2[] = new int[n];
		dist = new int[n];
		bfs(0,dist1,n);
		bfs(x,dist2,n);
		b = new boolean[n];
		dfs(0);
		int fa = 0;
		for(int i = 0; i< n;  i++){
			//System.out.println(i+" "+dist1[i]+" "+dist2[i] +" "+dist[i]);
			if(dist2[i]<dist1[i]){
				fa = Math.max(fa, 2*(dist1[i]+dist[i]-1));
			}
		}
		System.out.println(fa);
	}
	int dfs(int x){
		b[x] = true;
		int max = 0;
		for(int i : amp[x]){
			if(!b[i]){
				max = Math.max(dfs(i), max);
			}
		}
		return dist[x] = (1+max);
	}
	void bfs(int x, int dist[], int n){
		dist[x] = 0;
		Queue<Integer> q = new LinkedList<>();
		q.add(x);
		boolean b[] = new boolean[n];
		b[x]  = true;
		while(!q.isEmpty()){
			int y = q.poll();
			for(int i : amp[y])
			{
				if(!b[i]){
					dist[i] = dist[y]+1;
					q.add(i);
					b[i] = true;
				}
			}
		}
	}
	void buildGraph(int n){
		for(int i = 0; i<n ;i++){
			int x = ni() -1, y = ni()- 1;
			amp[x].add(y);
			amp[y].add(x);
		}
	}
	long get(int x){
		long val = 0;
		for(int i = 0; i< N; i++){
			val += Math.abs(x-arr[i]);
			x+=L;
		}
		return val;
	}
	void dfs(int i, int j){
		boo[i][j] = true;
		if(ch[i][j]=='F') return;
		Pair p = new Pair(i,j);
		if(i>0 && ch[i-1][j]!='*' && !boo[i-1][j]){
			parent[i-1][j] = p;
			dfs(i-1,j);
		}
		if(j>0 && ch[i][j-1]!='*' && !boo[i][j-1]){
			parent[i][j-1] = p;
			dfs(i,j-1);
		}
		if(i<N-1 && ch[i+1][j]!='*' && !boo[i+1][j]){
			parent[i+1][j] = p;
			dfs(i+1,j);
		}
		if(j<K-1 && ch[i][j+1]!='*' && !boo[i][j+1]){
			parent[i][j+1] = p;
			dfs(i,j+1);
		}
	}
	int recur(int n){
		//System.out.println(n);
		if(n>=N) return 0;
		if(DP[n]!=-1) return DP[n];
		int ans = 0;
		DP[n] = 0;
		
		for(int i = n; i<N;i++){
			if(start[arr[i]]>n){
				DP[i] = Math.max((red[end[arr[i]]]^red[start[arr[i]]-1]+recur(end[arr[i]])),DP[i]);
			}
			/*if(start[arr[i]]>i){
				ans = Math.max(ans,(red[end[arr[i]]]^red[start[arr[i]]-1]+recur(end[arr[i]])));
				if(arr[i]==2){
					System.out.println(i);
					System.out.println((red[end[arr[i]]]^red[start[arr[i]]-1])+"*");
					System.out.println(ans);
				}
			}*/
		}
		return DP[n];
	}
	void recur(int n, int k){
		if(k<0) return;
		hs.add(K-k);
		if(n>=0 && dp[n][k]!=-1) return;
		if(n>=0) dp[n][k] = 1;
		for(int i = n+1;i<N;i++){
			recur(i,k-arr[i]);
		}
	}
	long modInverse(long a, long mOD2){
        return  power(a, mOD2-2, mOD2);
	}
	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;
	}
	boolean isPrime(int x){
		for(int i = 2;i*1L*i<=x;i++) if(x%i==0) return false;
		return true;
	}
	public String isPossible(int b[]){
		String ans = "Possible";
		int n = b.length;
		Arrays.sort(b);
		if(n==1) return "Possible";
		if(b[0]==1) return "Impossible";
		if(b[0]>=n) return ans;
		int lcm = 1;
		for(int i : b){
			long gcd = gcd(lcm,i);
			lcm *= (i/gcd);
		}
		int cnt = 0;
		for(int i : b) cnt+=lcm/i;
		if(cnt>lcm) return "Impossible";
		return ans;
	}
	public long gcd(long a, long b){
		if(b==0) return a;
		return gcd(b,a%b);
	}
	void failFn(String str, int arr[]){
		int len = 0;
		arr[0] = 0;
		int i = 1;
		while(i<arr.length){
			if(str.charAt(i)==str.charAt(len)){
				arr[i++] = ++len;
				continue;
			}
			if(len == 0){
				arr[i] = len;
				i++;
				continue;
			}
			if(str.charAt(i)!=str.charAt(len)){
				len = arr[len-1];
			}
		}
	}
	static class ST1{
		int arr[], st[], size;
		ST1(int a[]){
			arr = a.clone();
			size = 10*arr.length;
			st = new int[size];
			build(0,arr.length-1,1);
		}
		void build(int ss, int se, int si){
			if(ss==se){
				st[si] = arr[ss];
				return;
			}
			int mid = (ss+se)/2;
			int val = 2*si;
			build(ss,mid,val); build(mid+1,se,val+1);
			st[si] = Math.min(st[val], st[val+1]);
		}
		int get(int ss, int se, int l, int r, int si){
			if(l>se || r<ss || l>r) return Integer.MAX_VALUE;
			if(l<=ss && r>=se) return st[si];
			int mid = (ss+se)/2;
			int val = 2*si;
			return Math.min(get(ss,mid,l,r,val), get(mid+1,se,l,r,val+1));
		}
	}
	static class ST{
		int arr[],lazy[],n;
		ST(int a){
			n = a;
			arr = new int[10*n];
			lazy = new int[10*n];
		}
		void up(int l,int r,int val){
			update(0,n-1,0,l,r,val);
		}
		void update(int l,int r,int c,int x,int y,int val){
			if(lazy[c]!=0){
				lazy[2*c+1]+=lazy[c];
				lazy[2*c+2]+=lazy[c];
				if(l==r)
					arr[c]+=lazy[c];
				lazy[c] = 0;
			}
			if(l>r||x>y||l>y||x>r)
				return;
			if(x<=l&&y>=r){
				lazy[c]+=val;
				return ;
			}
			int mid = l+r>>1;
			update(l,mid,2*c+1,x,y,val);
			update(mid+1,r,2*c+2,x,y,val);
			arr[c] = Math.max(arr[2*c+1], arr[2*c+2]);
		}
		int an(int ind){
			return ans(0,n-1,0,ind);
		}
		int ans(int l,int r,int c,int ind){
			if(lazy[c]!=0){
				lazy[2*c+1]+=lazy[c];
				lazy[2*c+2]+=lazy[c];
				if(l==r)
					arr[c]+=lazy[c];
				lazy[c] = 0;
			}
			if(l==r)
				return arr[c];
			int mid = l+r>>1;
			if(mid>=ind)
				return ans(l,mid,2*c+1,ind);
			return ans(mid+1,r,2*c+2,ind);
		}
	}
	public static class FenwickTree {
		
	    int[] array; // 1-indexed array, In this array We save cumulative information to perform efficient range queries and updates

	    public FenwickTree(int size) {
	        array = new int[size + 1];
	    }
	    public int rsq(int ind) {
	        assert ind > 0;
	        int sum = 0;
	        while (ind > 0) {
	            sum += array[ind];
	            //Extracting the portion up to the first significant one of the binary representation of 'ind' and decrementing ind by that number
	            ind -= ind & (-ind);
	        }
	        return sum;
	    }
	    public int rsq(int a, int b) {
	        assert b >= a && a > 0 && b > 0;
	        return rsq(b) - rsq(a - 1);
	    }
	    public void update(int ind, int value) {
	        assert ind > 0;
	        while (ind < array.length) {
	            array[ind] += value;
	            //Extracting the portion up to the first significant one of the binary representation of 'ind' and incrementing ind by that number
	            ind += ind & (-ind);
	        }
	    }
	    public int size() {
	        return array.length - 1;
	    }
	}
	public static int[] shuffle(int[] a, Random gen){
		for(int i = 0, n = a.length;i < n;i++)
		{ 
			int ind = gen.nextInt(n-i)+i; 
			int d = a[i]; 
			a[i] = a[ind];
			a[ind] = d; 
		} 
	return a; 
	}

	class Pair implements Comparable<Pair>{
		int u, v;
		Pair(int u, int v){
			this.u = u;
			this.v = v;
		}public int hashCode() {
			return Objects.hash();
		}
		public boolean equals(Object o) {
			Pair other = (Pair) o;
			return ((u == other.u && v == other.v) || (v == other.u && u == other.v));
		}
		public int compareTo(Pair other) {
			//return Integer.compare(val, other.val);
			return Long.compare(u, other.u);// != 0 ? (Long.compare(u, other.u)) : (Long.compare(v,other.v));
		}
	}
	long power(long x, long y, int mod){
		long ans = 1;
		while(y>0){
			if(y%2==0){
				x = (x*x)%mod;
				y/=2;
			}
			else{
				ans = (x*ans)%mod;
				y--;
			}
		}
		return ans;
	}
	void soln() {
		is = System.in;
		out = new PrintWriter(System.out);
		long s = System.currentTimeMillis();
		solve();
		//out.close();
		out.flush();
		//tr(System.currentTimeMillis() - s + "ms");
	}


	// To Get Input
	// Some Buffer Methods
	private byte[] inbuf = new byte[1024];
	public int lenbuf = 0, ptrbuf = 0;

	private int readByte() {
		if (lenbuf == -1)
			throw new InputMismatchException();
		if (ptrbuf >= lenbuf) {
			ptrbuf = 0;
			try {
				lenbuf = is.read(inbuf);
			} catch (IOException e) {
				throw new InputMismatchException();
			}
			if (lenbuf <= 0)
				return -1;
		}
		return inbuf[ptrbuf++];
	}

	private boolean isSpaceChar(int c) {
		return !(c >= 33 && c <= 126);
	}

	private int skip() {
		int b;
		while ((b = readByte()) != -1 && isSpaceChar(b))
			;
		return b;
	}

	private double nd() {
		return Double.parseDouble(ns());
	}

	private char nc() {
		return (char) skip();
	}
	private String ns() {
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while (!(isSpaceChar(b))) { // when nextLine, (isSpaceChar(b) && b != '
									// ')
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	private char[] ns(int n) {
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while (p < n && !(isSpaceChar(b))) {
			buf[p++] = (char) b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}

	private char[][] nm(int n, int m) {
		char[][] map = new char[n][];
		for (int i = 0; i < n; i++)
			map[i] = ns(m);
		return map;
	}

	private int[] na(int n) {
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = ni();
		return a;
	}

	private int ni() {
		int num = 0, b;
		boolean minus = false;
		while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
			;
		if (b == '-') {
			minus = true;
			b = readByte();
		}

		while (true) {
			if (b >= '0' && b <= '9') {
				num = num * 10 + (b - '0');
			} else {
				return minus ? -num : num;
			}
			b = readByte();
		}
	}

	private long nl() {
		long num = 0;
		int b;
		boolean minus = false;
		while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
			;
		if (b == '-') {
			minus = true;
			b = readByte();
		}

		while (true) {
			if (b >= '0' && b <= '9') {
				num = num * 10 + (b - '0');
			} else {
				return minus ? -num : num;
			}
			b = readByte();
		}
	}

	private boolean oj = System.getProperty("ONLINE_JUDGE") != null;

	private void tr(Object... o) {
		if (!oj)
			System.out.println(Arrays.deepToString(o));
	}
}