#include <bits/stdc++.h>
template <class T> using Vec = std::vector<T>;
template <class F> struct RecLambda : private F {
explicit RecLambda(F&& f) : F(std::forward<F>(f)) {}
template <class... Args> decltype(auto) operator() (Args&&... args) const {
return F::operator()(*this, std::forward<Args>(args)...);
}
};
int main() {
int N, T, M;
std::cin >> N >> T >> M;
T -= 1;
M -= 1;
Vec<Vec<int>> graph(N);
for (int i = 0; i < N - 1; ++i) {
int a, b;
std::cin >> a >> b;
a -= 1;
b -= 1;
graph[a].push_back(b);
graph[b].push_back(a);
}
Vec<int> parent(N, -1);
RecLambda([&](auto&& dfs, const int u) -> void {
for (const int v : graph[u]) {
if (parent[u] != v) {
parent[v] = u;
dfs(v);
}
}
})(T);
int ans = RecLambda([&](auto&& dfs, const int u) -> int {
int max = 0;
for (const int v : graph[u]) {
if (v != parent[u]) {
max = std::max(max, dfs(v));
}
}
return max + (int) graph[u].size() - 1;
})(M);
while (M != T) {
ans += 1;
M = parent[M];
}
std::cout << ans - 1 << '\n';
return 0;
}
