#include "bits/stdc++.h"
using namespace std;
#define ar array
typedef int64_t ll;
const int N = 1e6 + 5;
vector<int> edges[N];
int n, t, m, dp[N], is[N];
int res = 0;
void dfs(int u, int p = -1){
is[u] = (u == t);
vector<int> t;
for(auto x : edges[u]){
if(x == p) continue;
dfs(x, u);
is[u] |= is[x];
t.push_back(x);
}
edges[u] = t;
sort(t.begin(), t.end(), [&](int& i, int& j){
return dp[i] > dp[j];
});
if(t.empty()) dp[u] = 0;
else {
dp[u] = 1 + ((int)t.size() > 1 ? dp[t[1]] + 1 : 0) + max(0, (int)t.size() - 2);
}
}
signed main(){
ios::sync_with_stdio(0); cin.tie(0);
cin>>n>>t>>m;
if(t == m){
cout<<0<<"\n";
return 0;
}
for(int i=1;i<n;i++){
int a, b; cin>>a>>b;
edges[a].push_back(b);
edges[b].push_back(a);
}
dfs(m);
int pos = 0, res = 0;
while(m != t){
//~ cout<<m<<" "<<t<<endl;
pos++;
vector<int> t;
int c = -1;
for(auto x : edges[m]){
if(is[x]) { c = x; continue; }
t.push_back(x);
}
sort(t.begin(), t.end(), [&](int& i, int& j){
return dp[i] > dp[j];
});
if(pos >= (int)t.size()){
pos -= (int)t.size();
res += (int)t.size();
} else {
res += dp[t[pos]] + (int)t.size();
pos = 1e9;
}
m = c;
}
cout<<res<<"\n";
}
/*
8 7 1
1 2
2 3
3 4
3 5
3 6
4 7
4 8
*/
