#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], pr[N];
void dfs(int v, int p, int wt){
vector<int> w;
for(int ch : g[v]){
if(ch == p) continue;
pr[ch] = v;
dfs(ch, v, (v == 1 ? 0 : wt + g[v].size()-2));
w.push_back(dp[ch]);
}
sort(w.rbegin(), w.rend());
dp[v] = (w.size() >= 2 ? w[1]+1 : wt);
if(w.size() == 1) dp[v]++;
}
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, 0);
int lo = 0, hi = 1e7;
while(lo < hi){
int wt = (lo+hi)/2;
int v = m, pv = 0, b = 0, d = 1, tf = 1;
while(v != t){
for(int ch : g[v]){
if(ch == pr[v] or ch == pv or dp[ch] < wt) continue;
if(b >= d) tf = 0;
b++;
}
pv = v;
v = pr[v];
d++;
}
if(tf) hi = wt;
else lo = wt+1;
}
int v = m, pv = 0, b = 0;
while(v != t){
for(int ch : g[v]){
if(ch == pr[v] or ch == pv) continue;
if(dp[ch] == lo-1){
cout<<b+lo - (v != m ? 1 : 0);
return;
}
if(dp[ch] >= lo) b++;
}
pv = v;
v = pr[v];
}
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);cout.tie(NULL);
int t = 1;
//cin>>t;
while(t--) solve();
return 0;
}
