// #pragma GCC optimize("O3,Ofast,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define MP make_pair
#define pb push_back
#define REP(i,n) for(int i = 0; (i) < (n); (i)++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
void fastio() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
}
const double EPS = 0.00001;
const int INF = 1e9+500;
const int N = 1e6 + 5;
const int ALPH = 26;
const int LGN = 25;
constexpr int MOD = 1e9+7;
int n,t,m;
vector<int> dp(N, 0);
vector<vector<int> > adj(N, vector<int>());
vector<array<int, 2> > vs;
void dfs(int node, int par) {
for(auto c : adj[node]) {
if(c == par) continue;
dfs(c, node);
}
array<int, 2> mx = {0, 0};
for(auto c : adj[node]) {
if(c == par) continue;
if(dp[c] > mx[0]) {
swap(mx[0], mx[1]);
mx[0] = dp[c];
}
else if(dp[c] > mx[1]) {
mx[1] = dp[c];
}
}
dp[node] = mx[1] + (int)adj[node].size() - 1;
}
int dfs2(int node, int par, int dist = 0) {
if(node == t) {
return node;
}
int ret = 0;
for(auto c : adj[node]) {
if(c == par) continue;
ret = dfs2(c, node, dist + 1);
if(ret) {
break;
}
}
if(!ret) return 0;
for(auto c : adj[node]) {
if(c == par || c == ret) continue;
dfs(c, node);
vs.pb({dp[c], dist});
// cout << "c:" << c << " dp:" << dp[c] << " dist:" << dist << "\n";
}
return node;
}
inline void solve() {
cin>>n>>t>>m;
REP(i, n - 1) {
int u, v;
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
dfs2(m, 0);
sort(rall(vs));
int ans = (int)vs.size();
set<int> slot;
for(int i = 0; i < n; i++) {
slot.insert(i);
}
for(auto &c : vs) {
auto itr = slot.upper_bound(c[1]);
if(itr == slot.begin()) {
ans += c[0];
break;
}
itr--;
slot.erase(itr);
}
cout << ans << "\n";
}
signed main() {
fastio();
int test = 1;
//cin>>test;
while(test--) {
solve();
}
}
