#include <bits/stdc++.h>
#include "race.h"
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-O3")
#pragma GCC target("avx2")
using namespace std;
#define pb push_back
#define sz size()
#define all(x) x.begin(), x.end()
#define F first
#define S second
typedef pair < int, int > pii;
typedef vector < int > vi;
typedef vector < vi > vvi;
const int N = 200200, A = 1000001;
vector <vector <pii> > g(N);
int _sz[N], used[N];
int mn[A];
void calc_sz (int v, int pr) {
_sz[v] = 1;
for (auto i : g[v]) {
int to = i.F;
if (used[to] || to == pr) {
continue;
}
calc_sz(to, v);
_sz[v] += _sz[to];
}
}
int get_centroid (int v, int pr, int n) {
for (auto i : g[v]) {
int to = i.F;
if (!used[to] && to != pr && _sz[to] > n / 2) {
return get_centroid(to, v, n);
}
}
return v;
}
int ans = 1e9;
vector <pii> vec;
void dfs (int v, int w, int pr, int d, int k) {
if (w > k) {
return;
}
int need = k - w;
if (need == 0) {
ans = min(ans, d);
}
if (mn[need] != 1e9) {
ans = min(ans, mn[need] + d);
}
vec.pb({w, d});
for (auto i : g[v]) {
int to = i.F, w1 = i.S;
if (used[to] || to == pr) {
continue;
}
dfs (to, w + w1, v, d + 1, k);
}
}
void calc_ans (int c, int k) {
calc_sz(c, c);
int v = get_centroid(c, c, _sz[c]);
used[v] = 1;
vector <pii> cur;
for (auto i : g[v]) {
int to = i.F, w = i.S;
if (used[to]) {
continue;
}
dfs (to, w, v, 1, k);
for(auto j : vec) {
mn[j.F] = min(mn[j.F], j.S);
cur.pb(j);
}
vec.clear();
}
for (auto i : cur) {
mn[i.F] = 1e9;
}
for (auto i : g[v]) {
int to = i.F;
if (used[to]) {
continue;
}
calc_ans(to, k);
}
}
int best_path (int N, int K, int h[][2], int l[]) {
int n = N;
int k = K;
for (int i = 0; i < n - 1; i++) {
int u = h[i][0], v = h[i][1], w = l[i];
g[u].pb({v, w});
g[v].pb({u, w});
}
for (int i = 0; i < A; i++) {
mn[i] = 1e9;
}
calc_ans(0, k);
if (ans == 1e9) {
ans = -1;
}
return ans;
}
