#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
using ull = unsigned long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
int dx[] = {1, 0, -1, 0, 1, -1, 1, -1};
int dy[] = {0, 1, 0, -1, 1, 1, -1, -1};
const int INT_INF = (int)(2e9);
const ll LL_INF = (ll)(2e18);
inline void fast_io() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
};
template <typename T, typename S>
inline ostream& operator<<(ostream& os, const pair<T, S> p) {
  cout << "[" << p.first << ";" << p.second << "]";
  return os;
}
template <typename T, typename S>
inline ostream& operator<<(ostream& os, const map<T, S> p) {
  for (auto el : p) cout << "[" << el.first << ";" << el.second << "]";
  return os;
}
template <typename T>
inline ostream& operator<<(ostream& os, const vector<T>& v) {
  for (auto el : v) cout << el << " ";
  return os;
}
template <typename T>
inline ostream& operator<<(ostream& os, const deque<T>& v) {
  for (auto el : v) cout << el << " ";
  return os;
}
template <typename T>
inline ostream& operator<<(ostream& os, const set<T>& v) {
  for (auto el : v) cout << el << " ";
  return os;
}
template <typename T>
inline vector<T> fetch_vec(int sz) {
  vector<T> ret(sz);
  for (auto& elem : ret) cin >> elem;
  return ret;
}
int N, u, v;
vector<vector<int>> G;
void input() {
  fast_io();
  cin >> N >> u >> v;
  u--, v--;
  G.resize(N);
  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);
  }
}
void bfs(int s, vector<int>& dp) {
  queue<int> q;
  q.push(s);
  dp[s] = 0;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (auto v : G[u]) {
      if (dp[v] >= 0) continue;
      dp[v] = dp[u] + 1;
      q.push(v);
    }
  }
}
int solve() {
  vector<int> A(N, -1), T(N, -1);
  bfs(u, T);
  bfs(v, A);
  int ans = 0;
  if (u == v) {
    cout << ans << endl;
    return 0;
  }
  for (int i = 0; i < N; i++) {
    if (T[i] >= A[i]) {
      ans = max(ans, A[i]);
      continue;
    }
    int tmp = T[i];
    int d = A[i] - T[i];
    if (d % 2)
      tmp += d;
    else
      tmp += d - 1;
    ans = max(ans, tmp);
  }
  cout << --ans << endl;
  return 0;
}
int main() {
  input();
  solve();
  return 0;
}
