#include <bits/stdc++.h>
using namespace std;
auto start = std::chrono::system_clock::now();
inline void skj() {
  std::chrono::time_point<std::chrono::system_clock> end;
  end = std::chrono::system_clock::now();
  std::chrono::duration<double> elapsed_seconds = end - start;
  std::time_t end_time = std::chrono::system_clock::to_time_t(end);
  cerr << "Time taken " << elapsed_seconds.count() * 1000 << "\n";
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
inline long long binexp(long long a, long long b, long long m) {
  if (a == 0) {
    return 0;
  }
  long long res = 1;
  a %= m;
  while (b) {
    if (b & 1) res = (res * 1ll * a) % m;
    a = (a * 1ll * a) % m;
    b >>= 1;
  }
  return res;
}
const long long N = 2e5 + 5;
long long level[N], mxl[N], pr[N];
vector<long long> g[N];
inline void dfs(long long s, long long p) {
  mxl[s] = level[s];
  pr[s] = p;
  for (long long i : g[s]) {
    if (i != p) {
      level[i] = level[s] + 1;
      dfs(i, s);
      mxl[s] = max(mxl[s], mxl[i]);
    }
  }
}
inline void solve_me_senpai() {
  long long n, u, v;
  cin >> n >> u >> v;
  for (long long i = 0; i < n - 1; i++) {
    long long a, b;
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  dfs(v, -1);
  long long d = (level[u] - level[v] - 1) / 2;
  while (d--) {
    u = pr[u];
  }
  v = pr[u];
  while (1) {
    long long mx = -1;
    for (long long x : g[v]) {
      if (x != pr[v]) {
        if (mx == -1 || (mxl[mx] < mxl[x])) {
          mx = x;
        }
      }
    }
    if (mx == -1) {
      break;
    }
    v = mx;
  }
  cout << level[v] - 1;
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long t = 1;
  long long a = 1;
  while (t--) {
    solve_me_senpai();
    a++;
  }
  return 0;
}
