#include<bits/stdc++.h>
using namespace std;
#define int long long
#define inf 5e18
#define nl '\n'
const int N = 1e6+1;
vector<int> g[N];
int dp[N];
void dfs(int v, int p){
vector<int> w;
for(int ch : g[v]){
if(ch == p) continue;
dfs(ch, v);
w.push_back(dp[ch]);
}
sort(w.rbegin(), w.rend());
dp[v] = (w.size() >= 2 ? w[1] : 0) + w.size();
}
inline void solve(){
int n, t, m;
cin>>n>>t>>m;
for(int i=1; i<n; i++){
int a, b;
cin>>a>>b;
g[a].push_back(b);
g[b].push_back(a);
}
dfs(t, 0);
cout<<dp[m]+1;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);cout.tie(NULL);
int t = 1;
//cin>>t;
while(t--) solve();
return 0;
}
