#include <bits/stdc++.h>
using namespace std;
using lint = long long;
using uli = unsigned long long;
uli gcd(uli a, uli b) {
  while (1) {
    if (a < b) swap(a, b);
    if (!b) break;
    a %= b;
  }
  return a;
}
uli lcm(uli a, uli b) { return a * b / gcd(a, b); }
const uli mod = 1000000007;
const double pi = 3.141592653589793238462;
const lint intmax = 9223372036854775807;
uli _PowMod(uli x, uli y, uli _mod) {
  if (y == 0) {
    return 1;
  } else if (y == 1) {
    return x % _mod;
  } else if (y % 2 == 0) {
    auto tmp = _PowMod(x, y / 2, _mod);
    return tmp * tmp % _mod;
  } else {
    auto tmp = _PowMod(x, y / 2, _mod);
    return (tmp * tmp % _mod) * x % _mod;
  }
}
uli PowMod(uli x, uli y) { return _PowMod(x, y, mod); }
uli getModInv(uli N) { return PowMod(N, mod - 2); }
lint nCrMod(lint start, lint n, lint r) {
  if (n < r) {
    return 0;
  }
  lint a = start;
  for (size_t i = n; i >= n - r + 1; i--) {
    a *= i;
    a %= mod;
  }
  for (size_t i = 1; i <= r; i++) {
    a *= getModInv(i);
    a %= mod;
  }
  return a;
}
lint nHrMod(lint start, lint n, lint r) { return nCrMod(start, n + r - 1, r); }
lint _nCrMod(lint start, lint n, lint r) {
  if (n <= 0) {
    return 0;
  }
  return nCrMod(start, n, r);
}
struct uf {
  vector<lint> p;
  uf(lint n) : p(n) {
    for (size_t i = 0; i < n; i++) {
      p[i] = i;
    }
  }
  lint rt(lint n) { return p[n] == n ? n : p[n] = rt(p[n]); }
  void un(lint n, lint m) { p[rt(n)] = p[rt(m)]; }
  bool eq(lint n, lint m) { return rt(n) == rt(m); }
};
bool lineCol(lint a1x, lint a1y, lint a2x, lint a2y, lint b1x, lint b1y,
             lint b2x, lint b2y) {
  auto ta = (b1x - b2x) * (a1y - b1y) + (b1y - b2y) * (b1x - a1x);
  auto tb = (b1x - b2x) * (a2y - b1y) + (b1y - b2y) * (b1x - a2x);
  auto tc = (a1x - a2x) * (b1y - a1y) + (a1y - a2y) * (a1x - b1x);
  auto td = (a1x - a2x) * (b2y - a1y) + (a1y - a2y) * (a1x - b2x);
  return tc * td < 0 && ta * tb < 0;
}
lint powInt(lint a, lint b) {
  if (b == 0) {
    return 1;
  }
  if (b == 1) {
    return a;
  }
  lint tmp = powInt(a, b / 2);
  return (b % 2 == 1 ? a * tmp * tmp : tmp * tmp);
}
lint _sMod(string n, lint mod) {
  lint k = (n[0] - '0') % mod;
  for (size_t i = 1; i < n.length(); i++) {
    k *= 10;
    k += (n[i] - '0');
    k %= mod;
  }
  return k;
}
template <typename T>
void vsort(vector<T>& v) {
  sort(v.begin(), v.end());
}
template <typename T>
void vsortr(vector<T>& v) {
  sort(v.rbegin(), v.rend());
}
lint div2(lint p, lint q) { return (p + q - 1) / q; }
struct xy {
  lint x, y;
  xy() : x(0), y(0) {}
  xy(lint _x, lint _y) : x(_x), y(_y) {}
};
int main() {
  lint n, u, v;
  cin >> n >> u >> v;
  u--;
  v--;
  vector<vector<lint>> r(n, vector<lint>(0));
  for (lint i = 0; i < n - 1; i++) {
    lint a, b;
    cin >> a >> b;
    r[a - 1].push_back(b - 1);
    r[b - 1].push_back(a - 1);
  }
  vector<lint> d(n);
  vector<lint> maxd(n);
  vector<lint> root(n, -1);
  {
    vector<lint> done(n, 0);
    lint now = v;
    d[now] = 0;
    while (1) {
      if (done[now] >= r[now].size() || r[now][done[now]] == root[now]) {
        done[now]++;
      }
      if (done[now] < r[now].size()) {
        lint next = r[now][done[now]];
        done[now]++;
        root[next] = now;
        d[next] = d[now] + 1;
        now = next;
      } else {
        if (now == v) {
          break;
        }
        if (done[now] == 1) {
          maxd[now] = d[now];
        }
        maxd[root[now]] = maxd[now];
        now = root[now];
      }
    }
  }
  lint w = u;
  if (d[u] == 1) {
    cout << 0 << endl;
    return 0;
  }
  while (1) {
    if (d[u] - d[root[w]] < d[root[w]]) {
      w = root[w];
    } else {
      break;
    }
  }
  cout << maxd[w] - 1 << endl;
  return 0;
}
