import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.NoSuchElementException;

public class Main {
	static int[][] edge;
	public static void main(String args[]) {
		FastScanner sc = new FastScanner();
		PrintWriter out = new PrintWriter(System.out);
		int N = sc.nextInt();
		int u = sc.nextInt();
		int v= sc.nextInt();
		edge = new int[N-1][N-1];
		for(int i=0;i<N;i++) {
			int a = sc.nextInt()-1;
			int b = sc.nextInt()-1;
			edge[a][b] = 1;
		}
		int result = dps(u,-1,v,0);
		result += dps2(v,0,0);
		out.println(result);



		out.flush();
	}

	static int dps(int now,int prev, int dest,int dist) {
		if(now==dest) return dist;
		else{
			for(int next: edge[now]) {
				if(next != prev) {;
					prev = now;
					return dps(next,prev, dest,dist+1);
				}
			}
		}
	}
	
	static int dps2(int now,int prev, int dist) {
		if(edge[now].length==1) return dist;
		for(int next: edge[now]) {
			if(next!=prev) {
				prev = now;
				return dps2(next,prev, dist);
			}
		}
	}
}

class FastScanner {
	private final InputStream in = System.in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;
	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		}else{
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}
	private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
	private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
	public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
	public String next() {
		if (!hasNext()) throw new NoSuchElementException();
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while(isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	public long nextLong() {
		if (!hasNext()) throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while(true){
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			}else if(b == -1 || !isPrintableChar(b)){
				return minus ? -n : n;
			}else{
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}
	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
		return (int) nl;
	}
	public double nextDouble() { return Double.parseDouble(next());}
}
}

