#include "race.h"
#include "bits/stdc++.h"
using namespace std;
#warning notusing64bitintegers
#define rep(i, a, b) for(int i = (a); i <= (b); ++i)
#define repd(i, a, b) for(int i = (a); i >= (b); --i)
#define em emplace
#define eb emplace_back
const int mxN = 200010;
const int mxK = 105;
vector<pair<int, int>> adj[mxN];
int dp[mxN][mxK], sm[mxN][mxK];
int ans = mxN;
void dfs(int x, int p, int K) {
dp[x][0] = 0;
for(auto [y, w] : adj[x]) {
if(y == p) continue;
dfs(y, x, K);
rep(i, w, K) {
if(dp[x][i] > 1 + dp[y][i - w]) {
sm[x][i] = dp[x][i];
dp[x][i] = 1 + dp[y][i - w];
}
else if(sm[x][i] > 1 + dp[y][i - w]) {
sm[x][i] = 1 + dp[y][i - w];
}
}
}
}
void solve(int x, int p, int K) {
ans = min(ans, dp[x][K]);
for(auto [y, w]: adj[x]) {
if(y == p) continue;
rep(l, w, K) {
int here = dp[y][l - w] + 1;
int there = dp[x][K - l];
if(K - l - w >= 0 && there == 1 + dp[y][K - l - w])
there = sm[x][K - l];
ans = min(ans, here + there);
}
solve(y, x, K);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
rep(i, 0, N - 2) {
adj[H[i][0] + 1].eb(H[i][1] + 1, L[i]);
adj[H[i][1] + 1].eb(H[i][0] + 1, L[i]);
}
rep(i, 0, N) rep(j, 0, K) dp[i][j] = sm[i][j] = mxN;
dfs(1, -1, K);
solve(1, -1, K);
if(ans >= N) ans = -1;
return ans;
}
