#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 1e6;
const int MAX_N2 = 1e3;
const int INF = 1e9;
bool onPathTM[MAX_N + 1];
int parent[MAX_N + 1];
int dpArb[MAX_N + 1];
int f[MAX_N + 1];
vector<int> adj[MAX_N + 1];
void dfs(int u, int p) {
parent[u] = p;
for (int v: adj[u]) {
if (v == p)
continue;
dfs(v, u);
}
}
void calcDp(int u, int p) {
int max1 = 0, max2 = 0;
int sons = 0;
for (int v: adj[u]) {
if (v == p)
continue;
calcDp(v, u);
if (!onPathTM[v]) {
if (dpArb[v] > max1) {
max2 = max1;
max1 = dpArb[v];
} else if (dpArb[v] > max2)
max2 = dpArb[v];
sons++;
}
}
dpArb[u] = sons + max2;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, t, m;
cin >> n >> t >> m;
for (int e = 0; e < n - 1; e++) {
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
dfs(t, 0);
int w = m;
vector<int> path;
while (w != t) {
onPathTM[w] = true;
path.push_back(w);
w = parent[w];
}
onPathTM[w] = true;
calcDp(t, 0);
int totalSons = 0;
vector<pair<int, int>> cand;
int k = path.size();
for (int i = m - 1; i >= 0; i--) {
int u = path[i];
for (int v: adj[u]) {
if (onPathTM[v])
continue;
totalSons++;
cand.push_back({dpArb[v], i});
}
}
sort(cand.begin(), cand.end());
reverse(cand.begin(), cand.end());
for (auto p: cand) {
int i = p.second;
bool done = false;
for (int j = i; j < k; j++) {
f[j]++;
done |= (f[j] > j + 1);
}
if (done) {
cout << p.first + totalSons << "\n";
return 0;
}
}
return 0;
}
