//Oh? You're Approaching Me?
#include <bits/stdc++.h>
//#include <fstream>
using namespace std;
//
#define int long long
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
// #pragma GCC optimize("O3,unroll-loops")
#define migmig ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define pb push_back
#define F first
#define S second
#define SZ(x) ll((x).size())
#define all(x) (x).begin(), (x).end()
#define cl clear
#define endl '\n'
#define deb(x) cerr << #x << " = " << x << '\n'
#define dokme(x) {cout << x << endl; return;}
#define wtf cout << "[ahaaaaaaaaaaaaaaaa]" << endl;
const int maxn = 2e5 + 100;
const int mod = 998244353;
const int inf = 1e18 + 5;
const int LOG = 61;
#define mid ((l + r) / 2)
#define lc (id * 2)
#define rc (lc + 1)
//g++ main.cpp -o main && main.exe
int n, m, t, dp[maxn];
vector<int> G[maxn];
void dfs(int u, int p) {
int childs = 0;
for (auto v : G[u])
if(v != p)
childs++;
if(childs == 0)
{
dp[u] = 0;
return;
}
int fir = 0, sec = 0;
for (auto v : G[u])
{
if(v == p)
continue;
dfs(v, u);
if(dp[v] > fir)
sec = fir, fir = dp[v];
else
if(dp[v] > sec)
sec = dp[v];
}
dp[u] = sec + childs;
return;
}
signed main() {
cin >> n >> t >> m;
for (int i = 1; i < n; i++) {
int v, u;
cin >> v >> u;
G[v].pb(u);
G[u].pb(v);
}
dfs(m, t);
cout << dp[m] << '\n';
}
