#include <bits/stdc++.h>
#define int long long
using namespace std;
const int nmax = 1e6 + 1;
int dp[nmax];
vector<int> adj[nmax];
void dfs(int i, int tata = 0) {
int minn = 1e9;
for(auto it : adj[i]) {
if(it == tata) {
continue;
}
dfs(it, i);
minn = min(minn, dp[it]);
}
if(adj[i].size() == 1) {
dp[i] = 0;
return;
}
dp[i] = minn + adj[i].size() - 1;
}
int32_t main() {
int n, ep, sp;
cin >> n >> ep >> sp;
for(int i = 1; i < n; i++) {
int a, b;
cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
dfs(ep);
cout << dp[sp];
return 0;
}
