#include<iostream>
#include<queue>
#include<stack>
#include<algorithm>
#include<string.h>
#define task
#define size() size() * 1ll
#define all(x) (x).begin(), (x).end()
#define allr(x, sz) (x) + 1, (x) + 1 + sz
#define pb push_back
#define pii pair<int,int>
#define fi first
#define se second
#define MASK(x) (1LL<<(x))
#define BIT(x,i) (((x)>>(i))&1)
#define numbit(x) __builtin_popcountll(x)
using namespace std;
const int N = 1e6 + 1;
const int M = 1e3 + 1;
const long long mod = 1e9 + 7;
const long long oo = 1e18 + 7;
typedef vector<int> vi;
typedef vector<pii> vii;
typedef long long ll;
template<class t>
bool mini(t &x,t y) {
if (x > y) {
x = y;
return 1;
}
return 0;
}
template<class t>
bool maxi(t &x,t y) {
if (x < y) {
x = y;
return 1;
}
return 0;
}
void file() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
//freopen(task.in, r, stdin);
//freopen(task.out, w, stdout);
return ;
}
int n, s, t;
int h[N], nxt[N];
vi a[N];
void dfs(int u, int chu) {
h[u] = 1;
for (auto v: a[u]) if (v != chu) {
dfs(v, u);
h[u] += h[v];
}
}
void solve(int test = -1) {
cin >> n >> s >> t;
for (int i = 1; i < n; i++) {
int x, y;
cin >> x >> y;
a[x].pb(y);
}
dfs(1, 0);
for (int i = 1; i <= n; i++) {
sort(all(a[i]), [&](const int &x, const int &y) {
return h[x] > h[y];
});
int k = a[i].size();
for (int j = 0; j < k - 1; j++) {
nxt[a[i][j]] = a[i][j + 1];
}
}
queue<int> q;
q.push(s);
q.push(t);
vi d(n + 1, -1);
d[s] = 0;
d[t] = 0;
while (!q.empty()) {
int u = q.front();
q.pop();
if (!u) continue;
if (u != s && u != t) {
int v = nxt[u];
if (v == s || v == t) v = nxt[v];
d[v] = d[u] + 1;
q.push(v);
}
if (a[u].size() < 1) continue;
int v = a[u][0];
if (v == s || v == t) v = nxt[v];
d[v] = d[u] + 1;
q.push(v);
}
cout << *max_element(all(d)) - 1;
}
int32_t main() {
file();
int T = 1;
// cin >> T;
for (int i = 1; i <= T; i++) {
solve(i);
}
return 0;
}
