#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize ("unroll-loops")
#define int long long
using namespace std;
typedef pair<int, int> pii;
typedef long long ll;
typedef long double ld;
#define X first
#define Y second
#define pb push_back
#define fastio ios_base::sync_with_stdio(0);cin.tie(nullptr);cout.tie(nullptr);
#define rndom mt19937 rng(chrono::steady_clock::now().time_since_epoch().count())
//#define endl '\n'
const int N = 1000 * 1000 + 5, inf = LLONG_MAX;
int n, m, t, par[N];
vector<int>adj[N];
int dp[N], r = -1, c = 1;
bool mark[N];
void dfs(int v, int p){
pii mx = {0, 0}; int ch = 0;
vector<int>vec;
for(int u : adj[v])if(u!=p && !mark[u]){
ch ++;
dfs(u, v);
if(v == r){
vec.pb(dp[u]);
continue;
}
if(dp[u] > mx.X){
pii tmp = {dp[u], mx.X};
mx = tmp;
}else if(dp[u] > mx.Y){
mx.Y = dp[u];
}
}
if(v == r){
while((int)vec.size() <= c)vec.pb(0);
sort(vec.begin(), vec.end(), greater<int>());
dp[v] = vec[c-1] + ch;
return;
}
if(ch == 0)return;
if(ch == 1){dp[v] = 1; return;}
dp[v] = ch + mx.Y;
return;
}
void path(int v, int p){
par[v] = p;
for(int u : adj[v])if(u!=p){
path(u,v);
}return;
}
int32_t main(){
///auto t = clock();
fastio;
cin >> n >> t >> m; m--; t --;
for(int i = 0; i < n -1; i ++){
int u, v;
cin >> u >> v;
v--; u --;
adj[u].pb(v); adj[v].pb(u);
}
path(m,-1);
mark[m] = 1;
vector<int>p;
int cur = t;
do{
//cout << "mark " << cur +1 << endl;
mark[cur] = 1;
p.pb(cur);
cur = par[cur];
}while(cur != -1);
reverse(p.begin(), p.end());
p.pop_back();
int ans = 0;
for(int u : p){
//cout << "dfs " << u+1 << ": ";
r = u;
c++;
dfs(u, -1);
//cout << dp[u] << endl;
ans += dp[u];
}
cout << ans << endl;
///cout << clock() - t << "ms" << endl;
return 0;
}
