#include "race.h"
#include <bits/stdc++.h>
using namespace std;
#define scd(t) scanf("%d", &t)
#define sclld(t) scanf("%lld", &t)
#define forr(i, j, k) for (int i = j; i < k; i++)
#define frange(i, j) forr(i, 0, j)
#define all(cont) cont.begin(), cont.end()
#define mp make_pair
#define pb push_back
#define f first
#define s second
typedef long long int lli;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<lli> vll;
typedef vector<string> vs;
typedef vector<pii> vii;
typedef vector<vi> vvi;
typedef map<int, int> mpii;
typedef set<int> seti;
typedef multiset<int> mseti;
typedef long double ld;
vector<vii> graph;
int n, k;
int out = 1e9;
vi sze;
vb vis;
int get_size(int x, int p=-1) {
sze[x] = 1;
for(auto e : graph[x]) {
if(e.f != p && !vis[e.f]) {
sze[x] += get_size(e.f, x);
}
}
return sze[x];
}
int get_cent(int x, int subsz, int p=-1) {
for(auto e : graph[x]) {
if(e.f != p && !vis[e.f] && 2*sze[e.f] > subsz) {
return get_cent(e.f, subsz, x);
}
}
return x;
}
map<lli, int> dist;
void dist_dfs(int x, int p, lli d, int d1) {
if(dist.find(d) == dist.end()) dist[d] = d1;
else dist[d] = min(dist[d], d1);
for(auto e : graph[x]) {
if(e.f != p && !vis[e.f]) {
dist_dfs(e.f, x, d+e.s, d1+1);
}
}
}
void decomp(int x) {
int sz = get_size(x);
x = get_cent(x, sz);
vis[x] = true;
map<lli, int> curr;
curr[0] = 0;
for(auto e : graph[x]) {
if(!vis[e.f]) {
dist = {};
dist_dfs(e.f, x, e.s, 1);
for(auto p : dist) {
auto it = curr.find(k-p.f);
if(it != curr.end()) {
out = min(out, p.s + (*it).s);
}
}
for(auto p : dist) {
if(curr.find(p.f) == curr.end()) curr[p.f] = p.s;
else curr[p.f] = min(curr[p.f], p.s);
}
}
}
for(auto e : graph[x]) {
if(!vis[e.f]) decomp(e.f);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
n = N;
k = K;
graph = vector<vii>(n);
frange(i, n-1) {
graph[H[i][0]].pb(mp(H[i][1], L[i]));
graph[H[i][1]].pb(mp(H[i][0], L[i]));
}
vis = vb(n+1);
sze = vi(n+1);
decomp(0);
if(out == 1e9) return -1;
return out;
}
