#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long
const int MAXN=1e6;
int DP[MAXN+1];
vector<vector<int>> graph(MAXN+1);
vector<int> path;
bool in[MAXN+1]={false};
bool getpath(int u,int p,int t){
path.push_back(u);
if(u==t){
return true;
}
for(int v:graph[u]){
if(v!=p){
if(getpath(v,u,t)){
return true;
}
}
}
path.pop_back();
return false;
}
void DFS(int u,int p){
DP[u]=0;
vector<int> child;
for(int v:graph[u]){
if(v!=p&&!in[v]){
DFS(v,u);
child.push_back(DP[v]+1);
}
}
sort(child.begin(),child.end(),greater<int>());
for(int i=0;i<child.size();i+=2){
child[i]=1;
}
for(int i=0;i<child.size();i++){
DP[u]+=child[i];
}
}
signed main(){
//freopen("mousetrap.inp","r",stdin);
//freopen("mousetrap.out","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n,t,root;
cin >> n >> t >> root;
for(int i=0;i<n-1;i++){
int u,v;
cin >> u >> v;
graph[u].push_back(v);
graph[v].push_back(u);
}
getpath(root,-1,t);
int ans=0;
for(int i=0;i<path.size();i++){
in[path[i]]=true;
}
for(int i=0;i+1<path.size();i++){
DFS(path[i],-1);
ans+=DP[path[i]];
}
cout << ans;
}
