#include <algorithm>
#include <bitset>
#include <cstdint>
#include <cstring>
#include <iostream>
#include <limits.h>
#include <math.h>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#define int long long
#define loop(X, N) for(int X = 0; X < (N); X++)
#define all(V) V.begin(), V.end()
#define rall(V) V.rbegin(), V.rend()
using namespace std;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<vector<ii>> vvii;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
int n, x, y, k;
vvii adj;
signed max_score(signed _n, signed _x, signed _y, int _k, vector<signed> u, vector<signed> v, vector<signed> w) {
n = _n; x = _x; y = _y; k = _k;
adj = vvii(n);
loop(i, n - 1) {
adj[u[i]].push_back({ v[i], w[i] });
adj[v[i]].push_back({ u[i], w[i] });
}
vi c(n, 0);
int score = 0;
typedef tuple<int, int, int> iii;
priority_queue<iii, vector<iii>, greater<iii>> todo;
todo.push({ 0, x, -1 });
todo.push({ 0, y, -1 });
while (todo.size()) {
auto [cost, node, parent] = todo.top();
todo.pop();
if (k - cost < 0)
break;
c[node] = cost;
k -= cost;
score++;
for (auto [child, weight] : adj[node]) {
if (child == parent)
continue;
todo.push({ cost + weight - c[child], child, node });
}
}
return score;
}
