#include<bits/stdc++.h>
using namespace std;
const int N = 1e6 + 5;
int dp[N];
int h[N];
bool viz[N];
vector<int> gr[N];
int par[N];
void first_dfs(int nod, int dad){
par[nod] = dad;
h[nod] = 1 + h[dad];
for(auto x:gr[nod]){
if(x != dad)
first_dfs(x, nod);
}
}
void dfs(int nod, int dad){
int nrvec = 0;
for(auto x:gr[nod]){
if(x == dad || viz[x] == true)
continue;
nrvec++;
dfs(x, nod);
}
if(nrvec == 1){
dp[nod] = 1;
return;
}
int m1 = 0, m2 = 0;
for(auto x:gr[nod]){
if(x == dad || viz[x])
continue;
if(nrvec + dp[x] > m1){
m2 = m1;
m1 = nrvec + dp[x];
}
else if(nrvec + dp[x] > m2){
m2 = nrvec + dp[x];
}
}
dp[nod] = m2;
}
int ans = 0;
int sm[N];
set<pair<pair<int, int>, int>> ms;
int solve(int nod){
viz[nod] = true;
if(par[nod] == 0)
return 0;
int sum = solve(par[nod]);
dfs(nod, 0);
ms.insert({{sum + dp[nod], h[nod]}, nod});
sm[nod] = sum + dp[nod];
sum += gr[nod].size() - (par[nod] != 0) - 1;
return sum;
}
void solvefr(int nod){
if(par[nod] == 0)
return;
ans = max(ans, sm[nod]);
ms.erase({{sm[nod], h[nod]}, nod});
if(ms.size()){
int id = (*ms.rbegin()).second;
ms.erase(*ms.rbegin());
sm[id] --;
ms.insert({{sm[id], h[id]}, id});
}
}
int main()
{
//freopen(".in","r",stdin);
ios::sync_with_stdio(false);
cin.tie(0),cout.tie(0);
int n, root, m;
cin>>n>>root>>m;
for(int i =1 ; i<n; i++){
int x, y;
cin>>x>>y;
gr[x].push_back(y);
gr[y].push_back(x);
}
first_dfs(root, 0);
solve(m);
solvefr(m);
cout<<ans;
return 0;
}
