#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define ll long long
#define pll pair<ll, ll>
#define pii pair<int, int>
#define mp(x, y) make_pair(x, y)
#define sz(v) ((int) (v).size())
#define all(v) (v).begin(), (v).end()
#define MASK(i) (1LL << (i))
#define BIT(x, y) (((x) >> (y)) & 1)
#define clz __builtin_clzll
#define ctz __builtin_ctzll
#define popcount __builtin_popcount
#define lg(x) (63 - clz(x))
#define max_rng *max_element
#define min_rng *min_element
template <class X, class Y>
inline bool maximize(X &x, Y y) {
return (x < y ? x = y, true : false);
}
template <class X, class Y>
inline bool minimize(X &x, Y y) {
return (x > y ? x = y, true : false);
}
template <class X>
inline void compress(vector<X> &a) {
sort(all(a)); a.resize(unique(all(a)) - a.begin());
}
const ll oo = (ll) 1e18, inf = (ll) 1e9, mod = (ll) 1e9 + 7;
const int mxn = (int) 1e6 + 5, S = (int) 450, S2 = (int) 450, lg = (int) 18;
void add(ll &x, ll y) {
x += y;
if (x >= mod) x -= mod;
}
void sub(ll &x, ll y) {
x -= y;
if (x < 0) x += mod;
}
int n, t, m;
vector<int> g[mxn];
int timer = 0;
int in[mxn], out[mxn];
int par[mxn], dist[mxn], h[mxn];
void dfs(int u, int p) {
in[u] = ++timer;
if (u != t) {
for (int v : g[u]) if (v != p)
dist[u]++;
}
for (int v : g[u]) if (v != p) {
dist[v] += dist[u];
h[v] = h[u] + 1;
dfs(v, u);
par[v] = u;
}
out[u] = timer;
}
bool inRoot(int r, int u) {
return in[r] <= in[u] && in[u] <= out[r];
}
int f[mxn], ban[mxn];
int dp(int u, int p, int blocked) {
if (f[u] != -1) return f[u];
int adj = 0;
for (int v : g[u]) if (v != p && !ban[v])
adj++;
if (adj <= blocked + 1) {
return f[u] = adj;
}
f[u] = inf;
int sz = g[u].size();
vector<int> k(sz, -inf), h(sz, -inf);
for (int i = 0; i < sz; ++i) {
int v = g[u][i];
if (v != p && !ban[v])
k[i] = h[i] = dp(v, u, blocked) + adj;
}
for (int i = 1; i < sz; ++i) {
maximize(k[i], k[i-1]);
}
for (int i = sz-2; i >= 0; --i) {
maximize(h[i], h[i+1]);
}
// cout << "PHASE BEGIN u = " << u << ' ' << p << '\n';
// for (int i = 0; i < sz; ++i) {
// int v = g[u][i];
// if (v != p && !ban[v]) {
// cout << i << ' ' << v << ' ' << k[i] << ' ' << h[i] << '\n';
// }
// }
for (int i = 0; i < sz; ++i) {
int v = g[u][i];
if (v == p || ban[v]) continue;
int cur = -inf;
if (i > 0) maximize(cur, k[i-1]);
if (i+1 < sz) maximize(cur, h[i+1]);
if (cur != -inf) minimize(f[u], cur);
}
return f[u];
}
int backtrack(int cur, int blocked = 0) {
if (cur == t) return -inf;
int res = dp(cur, par[cur], blocked);
res += dist[par[cur]] - h[par[cur]];
// cout << cur << ' ' << par[cur] << ' ' << blocked << ' ' << f[cur] << ' ' << dist[par[cur]] - h[par[cur]] << "\n\n\n";
ban[cur] = true; f[cur] = 0;
return max(res, backtrack(par[cur], blocked+1));
}
void solve() {
cin >> n >> t >> m;
for (int i = 2; i <= n; ++i) {
int u, v;
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
if (t == m) {
cout << 0 << '\n';
return;
}
memset(f, -1, sizeof f);
dfs(t, 0);
ll ans = backtrack(m);
assert(ans < inf);
cout << ans;
return;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
#define TASK "task"
if (fopen(TASK".inp", "r")) {
freopen(TASK".inp", "r", stdin);
freopen(TASK".out", "w", stdout);
}
int t = 1;
// cin >> t;
while (t--) {
solve();
}
// cerr << "\nTime elapsed: " << (1.0 * clock() / CLOCKS_PER_SEC) << " s.";
return 0;
}
