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.util.*;
import java.math.*;
import java.lang.*;

public class Main implements Runnable {
    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;
        private BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (numChars == -1)
                throw new InputMismatchException();

            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }

                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

        public String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }

        public int nextInt() {
            int c = read();

            while (isSpaceChar(c))
                c = read();

            int sgn = 1;

            if (c == '-') {
                sgn = -1;
                c = read();
            }

            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));

            return res * sgn;
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;

            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public double nextDouble() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') {
                c = read();
                double m = 1;
                while (!isSpaceChar(c)) {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, nextInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }

        public String readString() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } 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 String next() {
            return readString();
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }

    public static void main(String args[]) throws Exception {
        new Thread(null, new Main(), "Main", 1 << 27).start();
    }

    static class Pair {
        int f;
        int s;
        int p;
        PrintWriter w;

        // int t;

        Pair(int f, int s) {
            // Pair(int f,int s, PrintWriter w){
            this.f = f;
            this.s = s;
            // this.p = p;
            // this.w = w;
            // this.t = t;

        }

        public static Comparator<Pair> wc = new Comparator<Pair>() {
            public int compare(Pair e1, Pair e2) {

                // 1 for swap
                if (Math.abs(e1.f) - Math.abs(e2.f) != 0) {
                    // e1.w.println("**"+e1.f+" "+e2.f);
                    return (Math.abs(e1.f) - Math.abs(e2.f));
                } else {
                    // e1.w.println("##"+e1.f+" "+e2.f);
                    return (Math.abs(e1.s) - Math.abs(e2.s));
                }

            }
        };
    }

    public static ArrayList<Integer> sieve(int N) {
        int i, j, flag;

        ArrayList<Integer> p = new ArrayList<Integer>();

        for (i = 1; i < N; i++) {

            if (i == 1 || i == 0)
                continue;

            flag = 1;

            for (j = 2; j <= i / 2; ++j) {
                if (i % j == 0) {
                    flag = 0;
                    break;
                }
            }
            if (flag == 1) {
                p.add(i);
            }
        }
        return p;
    }

    public static long gcd(long a, long b) {
        if (b == 0)
            return a;
        else
            return gcd(b, a % b);
    }

    //// recursive dfs
    public static int dfs(int s, ArrayList<Integer>[] g, long[] dist, boolean[] v, PrintWriter w, int p) {
        v[s] = true;
        int ans = 1;
        // int n = dist.length - 1;
        int t = g[s].size();
        // int max = 1;
        for (int i = 0; i < t; i++) {
            int x = g[s].get(i);
            if (!v[x]) {
                // dist[x] = dist[s] + 1;
                ans = Math.min(ans, dfs(x, g, dist, v, w, s));
            } else if (x != p) {
                // w.println("* " + s + " " + x + " " + p);
                ans = 0;
            }
        }
        // max = Math.max(max,(n-p));
        return ans;
    }

    //// iterative BFS
    public static int bfs(int s, ArrayList<Integer>[] g, long[] dist, boolean[] b, PrintWriter w, int p) {
        b[s] = true;
        int siz = 1;
        // dist--;
        Queue<Integer> q = new LinkedList<>();
        q.add(s);
        while (q.size() != 0) {
            int i = q.poll();
            Iterator<Integer> it = g[i].listIterator();
            int z = 0;
            while (it.hasNext()) {
                z = it.next();
                if (!b[z]) {
                    b[z] = true;
                    // dist--;
                    dist[z] = dist[i] + 1;
                    // siz++;
                    q.add(z);
                } else if (z != p) {
                    siz = 0;
                }
            }

        }
        return siz;
    }

    public static int lower(int key, int[] a) {
        int l = 0;
        int r = a.length - 1;
        int res = 0;

        while (l <= r) {
            int mid = (l + r) / 2;

            if (a[mid] <= key) {
                l = mid + 1;
                res = mid + 1;
            } else {
                r = mid - 1;
            }
        }

        return res;
    }

    public 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;

        if (y % 2 == 0)
            return p;
        else
            return (x * p) % m;
    }

    //////////////////////////////////////////////////////////////////////////////////////////////////////
    //////////////////////////////////////////////////////////////////////////////////////////////////////
    // code here
    int[] parent;
    int[] dist;
    int[] height;
    boolean[] vis;
    ArrayList<Integer>[] g;

    public void run() {

        InputReader sc = new InputReader(System.in);
        PrintWriter w = new PrintWriter(System.out);
        int defaultValue = 0;
        int mod = 1000000007;
        int oo = (int) 1e9;

        int test = 1;
        // test = sc.nextInt();
        while (test-- > 0) {
            int n = sc.nextInt();
            int x = sc.nextInt();

            dist = new int[n + 1];
            height = new int[n + 1];
            vis = new boolean[n + 1];
            g = new ArrayList[n + 1];

            for (int i = 0; i <= n; i++) {
                g[i] = new ArrayList<Integer>();
            }

            for (int i = 0; i < n - 1; i++) {
                int u = sc.nextInt();
                int v = sc.nextInt();
                g[v].add(u);
                g[u].add(v);
            }
            sol(x, dist);
            Arrays.fill(vis, false);
            int[] dist2 = new int[n + 1];
            sol(1, dist2);
            Arrays.fill(vis, false);
            // sol2(1);

            int ans = 0;
            for (int i = 1; i <= n; i++) {
                if (dist2[i] > dist[i]) {
                    ans = Math.max(ans, 2 * (dist2[i]));
                }
            }
            w.println(ans);

        }

        w.flush();
        w.close();

    }

    public void sol(int s, int[] distt) {
        vis[s] = true;
        Queue<Integer> q = new LinkedList<Integer>();
        q.add(s);
        while (!q.isEmpty()) {
            int i = q.poll();
            for (int x : g[i]) {
                if (!vis[x]) {
                    vis[x] = true;
                    distt[x] = distt[i] + 1;
                    q.add(x);
                }
            }
        }
    }

    public int sol2(int s) {
        vis[s] = true;
        int max = -1;
        for (int x : g[s]) {
            if (!vis[x])
                max = Math.max(max, sol2(x));
        }
        height[s] = max + 1;
        return height[s];
    }

}
