//#include "race.h"
#include <bits/stdc++.h>
#define pii pair<int, int>
#define x first
#define y second
using namespace std;
const int N = 2e5 + 5;
const int M = 1e6 + 5;
int n, k;
int ans = -1, centroid, mxnode, cnt = 0;
int dep[N], path[M], dp[M];
vector<vector<pii> > g(N);
bitset<N> chk;
int subtree(int u, int p) {
dep[u] = 1;
for(pii v : g[u]) if(!chk[v.x] && v.x != p) {
dep[u] += subtree(v.x, u);
}
return dep[u];
}
void centdecomp(int u, int p, int all) {
int ret = all - dep[u];
for(pii v : g[u]) if(!chk[v.x] && v.x != p) {
centdecomp(v.x, u, all);
ret = max(ret, dep[v.x]);
}
if(ret < mxnode) centroid = u, mxnode = ret;
}
void dfs(int u, int p, int cost, int edge, bool fill) {
if(cost > k) return;
if(!fill) {
if(dp[k - cost] == cnt && (edge + path[k - cost] < ans || ans == -1)) ans = edge + path[k - cost];
if(cost == k && (edge < ans || ans == -1)) ans = edge;
} else if(dp[cost] < cnt || edge < path[cost]) dp[cost] = cnt, path[cost] = edge;
for(pii v : g[u]) if(!chk[v.x] && v.x != p) {
dfs(v.x, u, cost + v.y, edge + 1, fill);
}
}
void proc(int u) {
cnt++;
if(subtree(u, -1) <= 1) return;
mxnode = dep[u] + 1;
centdecomp(u, -1, dep[u]);
for(pii v : g[centroid]) if(!chk[v.x]) {
dfs(v.x, centroid, v.y, 1, false);
dfs(v.x, centroid, v.y, 1, true);
}
chk[centroid] = 1;
for(pii v : g[centroid]) if(!chk[v.x]) {
proc(v.x);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
n = N, k = K;
for(int i = 0; i < N - 1; i++) {
g[H[i][0]].emplace_back(H[i][1], L[i]);
g[H[i][1]].emplace_back(H[i][0], L[i]);
}
proc(0);
return ans;
}
