We have a tree with N vertices. The i-th edge connects Vertex A_i and B_i bidirectionally.

Takahashi is standing at Vertex u, and Aoki is standing at Vertex v.

Now, they will play a game of tag as follows:

* 1. If Takahashi and Aoki are standing at the same vertex, the game ends. Otherwise, Takahashi moves to a vertex of his choice that is adjacent to his current vertex.

* 2. If Takahashi and Aoki are standing at the same vertex, the game ends. Otherwise, Aoki moves to a vertex of his choice that is adjacent to his current vertex.

* 3. Go back to step 1.




Takahashi performs his moves so that the game ends as late as possible, while Aoki performs his moves so that the game ends as early as possible.

Find the number of moves Aoki will perform before the end of the game if both Takahashi and Aoki know each other's position and strategy.

It can be proved that the game is bound to end.

Constraints

* 2 \leq N \leq 10^5
* 1 \leq u,v \leq N
* u \neq v
* 1 \leq A_i,B_i \leq N
* The given graph is a tree.

Input

Input is given from Standard Input in the following format:


N u v
A_1 B_1
:
A_{N-1} B_{N-1}


Output

Print the number of moves Aoki will perform before the end of the game.

Examples

Input

5 4 1
1 2
2 3
3 4
3 5


Output

2


Input

5 4 5
1 2
1 3
1 4
1 5


Output

1


Input

2 1 2
1 2


Output

0


Input

9 6 1
1 2
2 3
3 4
4 5
5 6
4 7
7 8
8 9


Output

5
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.*;

public class Main {
	static final long MOD=1000000007;//998244353;
	public static void main(String[] args) {
		PrintWriter out = new PrintWriter(System.out);
		InputReader sc=new InputReader(System.in);
		int N=sc.nextInt();
		int u=sc.nextInt()-1;
		int v=sc.nextInt()-1;
		graph G=new graph(N);
		for (int i = 0; i < N-1; i++) {
			int a=sc.nextInt()-1;
			int b=sc.nextInt()-1;
			G.addEdge(a, b, 1);
			G.addEdge(b, a, 1);
		}
		long[] d1=G.dijkstra(u);
		long[] d2=G.dijkstra(v);
		long max=-1;
		long ans=0;
		for (int i = 0; i < d2.length; i++) {
			if (d1[i]<d2[i]){
				if (max<d2[i]) {
					max=d2[i];
				}
			}
		}
		System.out.println(max-1);
	}
	static class Edge implements Comparable<Edge>{
		int to;
		long v;
		public Edge(int to,long v) {
			this.to=to;
			this.v=v;
		}
		@Override
    	public boolean equals(Object obj) {
    		if(obj instanceof Edge) {
    			Edge other = (Edge) obj;
    			return other.to==this.to && other.v==this.v;
    		}
    		return false;
    	}//同値の定義
    	@Override
    	public int hashCode() {
    		return Objects.hash(this.to,this.v);
    	}
    	@Override
		  public int compareTo( Edge p2 ){
			 if (this.v>p2.v) {
				return 1;
			}
			 else if (this.v<p2.v) {
				return -1;
			}
			 else {
				return 0;
			}
		  }
	} 
	static class graph{
		ArrayList<Edge>[] list;
		int size;
		long INF=Long.MAX_VALUE/2;
		int[] color;
		@SuppressWarnings("unchecked")
		public graph(int n) {
			size = n;
			list = new ArrayList[n];
			color =new int[n];
			for(int i=0;i<n;i++){
				list[i] = new ArrayList<Edge>();
			}
		}
		void addEdge(int from,int to,long w) {
			list[from].add(new Edge(to,w));
		}
		long[] dijkstra(int s){
	        long[] L = new long[size];
	        for(int i=0;i<size;i++){
	            L[i] = -1;
	        }
	        int[] visited = new int[size];
	        L[s] = 0;
	        PriorityQueue<Edge> Q = new PriorityQueue<Edge>();
	        Q.add(new Edge(s,0L));//Edgeに最短距離候補を持たせる
	        while(!Q.isEmpty()){
	            Edge C = Q.poll();
	            if(visited[C.to]==0){
	                L[C.to] = C.v;
	                visited[C.to] = 1;
	                for(Edge D:list[C.to]){
	                    Q.add(new Edge(D.to,L[C.to]+D.v));
	                }
	            }
	        }
	        return L;
	    }
		long[] bfs(int s) {
			long[] l=new long[size];
			for (int i = 0; i < l.length; i++) {
				l[i]=-1;
			}
			l[s]=0;
			ArrayDeque<Integer> qArrayDeque=new ArrayDeque<Integer>();
			qArrayDeque.add(s);
			while (!qArrayDeque.isEmpty()) {
				int v=qArrayDeque.poll();
				for (Edge nv: list[v]) {
					if (l[nv.to]==-1) {
						l[nv.to]=l[v]+nv.v;
						qArrayDeque.add(nv.to);
					}
				}
			}
			return l;
		}
	}
	static class InputReader { 
		private InputStream in;
		private byte[] buffer = new byte[1024];
		private int curbuf;
		private int lenbuf;
		public InputReader(InputStream in) {
			this.in = in;
			this.curbuf = this.lenbuf = 0;
		}
 
		public boolean hasNextByte() {
			if (curbuf >= lenbuf) {
				curbuf = 0;
				try {
					lenbuf = in.read(buffer);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (lenbuf <= 0)
					return false;
			}
			return true;
		}
 
		private int readByte() {
			if (hasNextByte())
				return buffer[curbuf++];
			else
				return -1;
		}
 
		private boolean isSpaceChar(int c) {
			return !(c >= 33 && c <= 126);
		}
 
		private void skip() {
			while (hasNextByte() && isSpaceChar(buffer[curbuf]))
				curbuf++;
		}
 
		public boolean hasNext() {
			skip();
			return hasNextByte();
		}
 
		public String next() {
			if (!hasNext())
				throw new NoSuchElementException();
			StringBuilder sb = new StringBuilder();
			int b = readByte();
			while (!isSpaceChar(b)) {
				sb.appendCodePoint(b);
				b = readByte();
			}
			return sb.toString();
		}
 
		public int nextInt() {
			if (!hasNext())
				throw new NoSuchElementException();
			int c = readByte();
			while (isSpaceChar(c))
				c = readByte();
			boolean minus = false;
			if (c == '-') {
				minus = true;
				c = readByte();
			}
			int res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res = res * 10 + c - '0';
				c = readByte();
			} while (!isSpaceChar(c));
			return (minus) ? -res : res;
		}
 
		public long nextLong() {
			if (!hasNext())
				throw new NoSuchElementException();
			int c = readByte();
			while (isSpaceChar(c))
				c = readByte();
			boolean minus = false;
			if (c == '-') {
				minus = true;
				c = readByte();
			}
			long res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res = res * 10 + c - '0';
				c = readByte();
			} while (!isSpaceChar(c));
			return (minus) ? -res : res;
		}
 
		public double nextDouble() {
			return Double.parseDouble(next());
		}
 
		public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for (int i = 0; i < n; i++)
				a[i] = nextInt();
			return a;
		}
 
		public long[] nextLongArray(int n) {
			long[] a = new long[n];
			for (int i = 0; i < n; i++)
				a[i] = nextLong();
			return a;
		}
 
		public char[][] nextCharMap(int n, int m) {
			char[][] map = new char[n][m];
			for (int i = 0; i < n; i++)
				map[i] = next().toCharArray();
			return map;
		}
	}
	}
