#include <bits/stdc++.h>
using namespace std;
using lint = long long;
constexpr int MOD = 1000000007, INF = 1010101010;
constexpr lint LINF = 1LL << 60;
template <class T>
ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (const auto &e : vec) os << e << (&e == &vec.back() ? "\n" : " ");
  return os;
}
template <class T>
void dump(const char *str, T &&h) {
  cerr << str << " = " << h << "\n";
};
template <class Head, class... Tail>
void dump(const char *str, Head &&h, Tail &&...t) {
  while (*str != ',') cerr << *str++;
  cerr << " = " << h << "\n";
  dump(str + (*(str + 1) == ' ' ? 2 : 1), t...);
}
template <typename T>
class segtree {
 private:
  int n, sz;
  vector<pair<T, int>> node;

 public:
  void resize(vector<T> &v) {
    sz = (int)v.size();
    n = 1;
    while (n < sz) {
      n *= 2;
    }
    node.resize(2 * n);
    for (int i = 0; i < sz; i++) {
      node[i + n] = make_pair(v[i], i);
    }
    for (int i = n - 1; i >= 1; i--) {
      node[i] = min(node[2 * i], node[2 * i + 1]);
    }
  }
  void update(int k, T a) {
    node[k += n] = make_pair(a, k);
    while (k >>= 1) {
      node[k] = min(node[2 * k], node[2 * k + 1]);
    }
  }
  pair<T, int> query(int a, int b) {
    pair<T, int> res1 = make_pair(numeric_limits<T>::max(), -1);
    pair<T, int> res2 = make_pair(numeric_limits<T>::max(), -1);
    a += n, b += n;
    while (a != b) {
      if (a % 2) res1 = min(res1, node[a++]);
      if (b % 2) res2 = min(res2, node[--b]);
      a >>= 1, b >>= 1;
    }
    return min(res1, res2);
  }
};
class LCA {
 private:
  int V;
  vector<vector<int>> G;
  vector<int> ord, depth, id;
  segtree<int> st;
  void dfs(int u, int p, int k) {
    id[u] = (int)ord.size();
    ord.push_back(u);
    depth[u] = k;
    for (int v : G[u]) {
      if (v != p) {
        dfs(v, u, k + 1);
        ord.push_back(u);
      }
    }
  }

 public:
  LCA(int node_size) : V(node_size), G(V), depth(V), id(V, -1) {}
  LCA(vector<vector<int>> G)
      : V(G.size()), G(G), depth(G.size()), id(G.size(), -1) {}
  void add_edge(int from, int to) {
    G[from].push_back(to), G[to].push_back(from);
  }
  void build() {
    ord.reserve(2 * V - 2);
    for (int i = 0; i < V; i++) {
      if (id[i] < 0) {
        dfs(i, -1, 0);
      }
    }
    vector<int> stvec(2 * V - 2);
    for (int i = 0; i < 2 * V - 2; i++) {
      stvec[i] = depth[ord[i]];
    }
    st.resize(stvec);
  }
  int lca(int u, int v) {
    dump("st.query(min(id[u], id[v]), max(id[u], id[v]) + 1).second",
         st.query(min(id[u], id[v]), max(id[u], id[v]) + 1).second);
    return ord[st.query(min(id[u], id[v]), max(id[u], id[v]) + 1).second];
  }
  int dist(int u, int v) {
    int lca_ = lca(u, v);
    return depth[u] + depth[v] - 2 * depth[lca_];
  }
};
int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int N;
  cin >> N;
  int t, a;
  cin >> t >> a;
  t--, a--;
  vector<vector<int>> edges(N);
  for (int i = 0; i < N - 1; i++) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    edges[u].emplace_back(v);
    edges[v].emplace_back(u);
  }
  LCA tree(edges);
  tree.build();
  int lca_i = tree.lca(t, a);
  dump("lca_i", lca_i);
  if (tree.dist(lca_i, t) <= tree.dist(lca_i, a)) {
    cout << tree.dist(t, a) - 1 << "\n";
  } else {
    exit(0);
    int max_d = 0;
    for (int i = 0; i < N; i++) {
      max_d = max(max_d, tree.dist(i, a));
    }
    cout << max_d - 1 << "\n";
  }
  return 0;
}
