#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <complex>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <vector>
using namespace std;
#define int long long
#define all(x) begin(x), end(x)
#define sz(x) (int) (x).size()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int mxn=1e6+1;

int n,t,m;
vector<int> adj[mxn];
int dp[mxn];

void dfs(int v,int p) {
	auto it=find(all(adj[v]),p);
	if (it!=adj[v].end()) adj[v].erase(it);
	if (!sz(adj[v])) return;
	vector<int> cdp = {0};
 	for (int u:adj[v]) {
		dfs(u,v);
		cdp.push_back(dp[u]);
		sort(all(cdp),greater<int>());
		cdp.resize(2);
	}
	dp[v] = sz(adj[v])+cdp[1];
}

signed main() {
	ios::sync_with_stdio(false); cin.tie(nullptr);
	
	cin>>n>>t>>m;
	for (int i=1; i<n; i++) {
		int u,v; cin>>u>>v; --u; --v;
		adj[u].push_back(v); adj[v].push_back(u);
	}
	dfs(t-1,t-1);
	cout<<dp[m-1]<<"\n";
	
	return 0;
}