#include "race.h"
#include <vector>
#include <algorithm>
#include <unordered_map>
using namespace std;
const int MAXN = 200005;
struct EDGE { int x, w; };
int N, K, ans = -1;
vector <EDGE> v[MAXN];
void f(int x, int par, unordered_map <int, int> &d, int &L, int &W) {
d[0] = 0;
for (auto &y : v[x]) {
if (y.x == par) continue;
unordered_map <int, int> d2;
int L2 = 0, W2 = 0;
f(y.x, x, d2, L2, W2);
L2++; W2 += y.w;
if (d.size() < d2.size()) {
d.swap(d2);
swap(L, L2);
swap(W, W2);
}
for (auto &t : d2) {
if (d.count(K - (t.first + W2 + W))) {
if (ans == -1 || ans > d[K - (t.first + W2 + W)] + t.second + L + L2)
ans = d[K - (t.first + W2 + W)] + t.second + L + L2;
}
}
for (auto &t : d2) {
if (t.first + W2 > K) continue;
if (t.first + W2 == K) {
if (ans == -1 || ans > t.second + L2)
ans = t.second + L2;
}
if (d.count(t.first + W2 - W)) d[t.first + W2 - W] = min(d[t.first + W2 - W], t.second + L2 - L);
else d[t.first + W2 - W] = t.second + L2 - L;
}
}
}
int best_path(int _N, int _K, int H[][2], int L[]) {
N = _N, K = _K;
for (int i = 0; i < N - 1; i++) {
v[H[i][0]].push_back({ H[i][1], L[i] });
v[H[i][1]].push_back({ H[i][0], L[i] });
}
unordered_map <int, int> d;
int A = 0, B = 0;
f(0, -1, d, A, B);
return ans;
}
