// Goods things are coming, just keep believing 
 
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace __gnu_pbds;
using namespace std;
 
 
#define FOR(i, x, n) for(ll i = x; i < n; i++) 
#define pb push_back
#define pf push_front
#define ll unsigned long long
#define hii cout << "hii" << endl
#define okay cout << "okay" << endl
// #define hey cout << "hey" << endl
#define pii pair<int, int>
#define pll pair<ll, ll>
// #define mpp make_pair
#define endl '\n'
#define ff first 
#define int long long
#define ss second
#define vi vector<int>
#define all(s) s.begin(), s.end()
#define si size()
 #define ld long double
#define INF 1000000000;
 
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
#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx2,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define _CRT_SECURE_NO_WARNINGS
#endif // ifndef ONLINE_JUDGE
 
typedef tree<
int,
null_type,
less<int>,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
 
 
 
const int N = 2e5 + 5;
const int LG = 20;
const int mod = 1e9 + 7;

int arr[N];

int n, m;
int diff[N];
int pref[N];

int h[N];
int parent[N];
vector<int> v[N];
int dp[N];

void dfs(int sv, int par, int lvl)
{
	h[sv] = lvl;
	parent[sv] = par;
	dp[sv] = lvl;
	for(int x : v[sv])
	{
		if(x != par)
		{
			dfs(x, sv, lvl + 1);
			dp[sv] = max(dp[sv], dp[x]);
		}
	}
}

void solve()
{
	int u, v;
	cin >> n >> u >> v;
	int t = n - 1;
	while(t--)
	{
		int a, b;
		cin >> a >> b;
		::v[a].push_back(b);
		::v[b].push_back(a);
	}
	if(u == v)
	{
		cout << 0 << endl;
		return;
	}
	dfs(v, 0, 1);
	int sv = 1;
	int ret = 0;
	int movea = 0;
	int moveb = 0;
	while(true)
	{
		int uu = dp[u] - h[u];
		int vv = dp[u] - moveb - 1;
		if(h[u] < moveb)
		{
			break;
		}
		// trace(uu, vv);
		if(h[u] == moveb)
		{
			ret = max(ret, moveb);
			break;
		}
		int moves = moveb;
		if(uu % 2 == vv % 2)
		{
			moves += ((vv - 1));
		}
		else
		{
			moves += (vv - 1);
		}
		if(moves == 0)
		{
			break;
		}
		// trace(moves);
		ret = max(moves, ret);
		moveb++;
		u = parent[u];
	}
	cout << ret << endl;
}
 
int32_t main()
{
	ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
	int t = 1;
	// cin >> t;
	while(t--)
	{
		solve();
	}
}

Measured memory_bytes: 18176