#include <bits/stdc++.h> using namespace std; typedef long long ll; typedef pair<int,int> pii; #define fi first #define se second #define mp make_pair #define fastIO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0); const int N = (int)1e6 + 100; vector<int> T[N]; int trap; int mouse; int dfs(int u, int par, int cum){ vector<int> lis; int deg = 0; for(auto x : T[u]){ if(x==par) continue; deg ++ ; } for(auto x : T[u]){ if(x==par) continue; lis.push_back(dfs(x,u,cum+deg)); } sort(lis.begin(), lis.end()); if(lis.size() <= 1){ return cum; } return lis[(int)lis.size() - 2]; } int main(){ fastIO; int n; cin >> n; cin >> trap >> mouse; int u, v; for(int i = 1; i < n; i ++ ){ cin >> u >> v; T[u].push_back(v); T[v].push_back(u); } cout << dfs(mouse,trap,0); return 0; }