#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <numeric>
#include <utility>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <unordered_map>
using namespace std;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

template<class T> vector<T> make_vec(size_t a) { return vector<T>(a); }
template<class T, class... Ts> auto make_vec(size_t a, Ts... ts) {
  return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}
template<class T, class V>
typename enable_if<is_class<T>::value == 0>::type fill(T &t, const V &v) {
    t = v;
}
template<class T, class V>
typename enable_if<is_class<T>::value != 0>::type fill(T &t, const V &v){
    for (auto &e : t) fill(e, v);
}

#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P)
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P)
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T> ostream& operator << (ostream &s, vector<vector<T> > P)
{ for (int i = 0; i < P.size(); ++i) { s << endl << P[i]; } return s << endl; }

#define EACH(i, s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)
template<class T> ostream& operator << (ostream &s, set<T> P)
{ EACH(it, P) { s << "<" << *it << "> "; } return s << endl; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P)
{ EACH(it, P) { s << "<" << it->first << "->" << it->second << "> "; } return s << endl; }





using Graph = vector<vector<int>>;
int N, v, r;
Graph G;

vector<int> par;
vector<int> depth;
vector<int> height;
vector<int> bestch;

void rec(int v, int d = 0, int p = -1) {
    par[v] = p;
    depth[v] = d;
    height[v] = 0;
    for (auto ch : G[v]) {
        if (ch == p) continue;
        rec(ch, d+1, v);
    }
    for (auto ch : G[v]) {
        if (chmax(height[v], height[ch] + 1)) {
            bestch[v] = ch;
        }
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    while (cin >> N >> v >> r) {
        --v, --r;
        G.assign(N, vector<int>());
        par.assign(N, -1);
        depth.resize(N);
        height.resize(N);
        bestch.assign(N, -1);
        for (int i = 0; i < N-1; ++i) {
            int a, b; cin >> a >> b; --a, --b;
            G[a].push_back(b);
            G[b].push_back(a);
        }

        rec(r);

        //COUT(par);COUT(bestch);COUT(depth);
        
        int res = 0;
        while (true) {
            // 上へ
            if (depth[v] > res + 2) {
                v = par[v];
                ++res;
            }
            else {
                if (bestch[v] == -1) {
                    v = par[v];
                    if (depth[v] == res) break;
                    else {
                        ++res;
                        break;
                    }
                }
                else {
                    v = bestch[v];

                    if (depth[v] == res) break;
                    
                    ++res;

                    if (depth[v] == res) break;
                }
            }

            //cout << v << "(" << depth[v] << "), " << res << endl;
        }
        cout << res << endl;
    }
}


















Measured memory_bytes: 13696