#include <bits/stdc++.h>
#define el '\n'
#define fu(i, a, b) for (long long i = a; i <= b; ++i)
#define fd(i, a, b) for (long long i = a; i >= b; --i)
#define ff first
#define ss second
#define all(v) v.begin(), v.end()
#define sz(v) (ll)v.size()
#define mask(i) (1LL << i)
#define bit(x, i) ((x) >> (i) & 1)
using namespace std;
typedef int ll;
typedef unsigned long long ull;
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll Rand(ll l, ll r) {
return uniform_int_distribution<ll> (l, r) (rng);
}
ll last(ll msk) {return msk & (-msk);}
ll pop_cnt(ll msk) {return __builtin_popcountll(msk);}
ll ctz(ll msk) {return __builtin_ctzll(msk);}
ll lg(ll msk) {return 63 - __builtin_clzll(msk);}
template<class T1, class T2>
bool maximize(T1 &a, T2 b) {
if (a < b) {
a = b;
return true;
}
return false;
}
template<class T1, class T2>
bool minimize(T1 &a, T2 b) {
if (a > b) {
a = b;
return true;
}
return false;
}
template<class T>
void print(T &a, string sep = " ", string stop = "\n") {
for (auto x : a) cout << x << sep;
cout << stop;
}
template<class T>
void compress(vector<T> &v) {
sort(all(v));
v.resize(unique(all(v)) - v.begin());
}
const long long N = 1e6 + 27, base = 311, inf = 2e18, mod = 1e9 + 19972207;
ll n, t, m, timer, cur;
ll a[N], f[N], in[N], out[N], left[N];
vector<ll> adj[N];
void dfs(ll u, ll p) {
in[u] = ++timer;
vector<ll> tmp;
for (ll v : adj[u]) {
if (v == p) continue;
dfs(v, u);
if (u == t) {
if (in[v] <= in[m] && in[m] <= out[v]) {
cout << f[v];
exit(0);
}
}
f[u] += f[v];
if (in[v] > in[m] || in[m] > out[v]) {
f[u]++;
tmp.push_back(f[v]);
}
}
out[u] = timer;
if (in[u] <= in[m] && in[m] <= out[u] && tmp.empty()) cur++;
sort(all(tmp));
if (sz(tmp)) f[u] -= tmp.back();
fd(i, sz(tmp) - 2, 0) {
if (!cur) break;
cur--;
f[u] -= tmp[i];
}
}
signed main() {
// freopen("brentford40mu.inp", "r", stdin);
// freopen("brentford40mu.out", "w", stdout);
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> n >> t >> m;
if (t == m) return cout << 0, 0;
fu(i, 2, n) {
ll u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
dfs(t, 0);
// fu(i, 1, n) cout << f[i] << ' ';
// cout << f[t];
}
