#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> // Common file 
#include <ext/pb_ds/tree_policy.hpp> 
#include <functional> // for less 
#define pb push_back
#define For(i,s,e) for (ll i=(s); i<(e); i++)
#define Debug_array(a,n) for (ll i=(0); i<(n); i++) cout<<a[i]<<" "
#define Foe(i,s,e) for (ll i=(s); i<=(e); i++)
#define Fod(i,s,e) for (ll i=(s)-1; i>=(e); i--)
#define pii pair<ll,ll>
#define fi first
#define se second
#define endl "\n"
#define mp make_pair
#define big_prime 15486277
#define bigger_prime 179424697
#define biggest_prime 32416188691
//#define random_shuffle(indices.begin(), indices.end());
//std::random_device rd;
//std::mt19937 g(rd());
//std::shuffle(v.begin(), v.end(), g);
using namespace __gnu_pbds; 
using namespace std;
template <class T> ostream& operator << (ostream &os, const vector<T> &v) { for (T i : v) os << i << ' '; return os; }
template <class T> ostream& operator << (ostream &os, const set<T> &v) { for (T i : v) os << i << ' '; return os; }
template <class T, class S> ostream& operator << (ostream &os, const pair<T, S> &v) { os << v.first << ' ' << v.second; return os; }
// template <class T, class S> ostream& operator << (ostream &os, const unordered_map<T, S> &v) { for (auto i : v) os << '(' << i.first << "=>" << i.second << ')' << ' '; return os; }
 
#ifndef ONLINE_JUDGE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
    template <class Arg1> void __f(const char* name, Arg1&& arg1) { cerr << name << " : " << arg1 << endl; }
    template <class Arg1, class... Args>
    void __f(const char* names, Arg1&& arg1, Args&&... args) {
        const char* sep = strchr(names + 1, ',');
        cerr.write(names, sep - names) << " : " << arg1 << "  ";
        __f(sep + 1, args...);
    }
#else
#define trace(...) 0
#define _CRT_SECURE_NO_WARNINGS
#endif // ifndef ONLINE_JUDGE


typedef long long ll;
typedef tree<ll, null_type, less<ll>, rb_tree_tag,tree_order_statistics_node_update> ordered_set; 

#define Mod 1000000007
#define MAX 100100

ll n,u,v;
vector<ll> adj[MAX];
ll dist_u[MAX],dist_v[MAX];

void fill_u(ll s,ll p,ll d){
	dist_u[s] = d;
	for(ll x:adj[s]) if(x!=p){
		fill_u(x,s,d+1);
	}
	return;
}
ll parent[MAX];
void fill_v(ll s,ll p,ll d){
	dist_v[s] = d;
	parent[s] = p;
	for(ll x:adj[s]) if(x!=p){
		fill_v(x,s,d+1);
	}
	return;
}

ll depth[MAX];
ll dfs(ll s,ll p){
	depth[s] = 0;
	for(ll x:adj[s]) if(x!=p){
		depth[s] = max(dfs(x,s)+1,depth[s]);
	}
	return depth[s];
}

int main(){
	ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
	cin>>n>>u>>v;u--;v--;
	For(i,0,n-1){
		ll x,y;cin>>x>>y;x--;y--;
		adj[x].pb(y);
		adj[y].pb(x);
	}
	fill_u(u,-1,0);
	fill_v(v,-1,v);
	dfs(v,-1);

	ll d = dist_u[v]-1;

	ll ans = depth[u]+d , count = 0;
	ll p = parent[u];
	ll c = 1;
	while(count<(d-1)){
		ans = max(ans,c+depth[p]+(d-2*c));
		p = parent[p];
		count++;
		c++;
	}
	cout<<ans<<endl;































	
}