#include<bits/extc++.h>
using namespace std;
using namespace __gnu_pbds;
#define int long long
const int mxN = 1e6+5;
using pii = pair<int,int>;
vector<pii> tr[mxN];
int sbsz[mxN], seen[mxN], N, K, res = LLONG_MAX, within;
int gsb(int x, int p=-1) {
sbsz[x] = 1ll;
#define nn it.second
for(auto it : tr[x]) if(!seen[nn] && nn != p) sbsz[x] += gsb(nn, x);
return sbsz[x];
}
int gc(int x, int p=-1) {
for(auto it : tr[x]) if(!seen[nn] && nn != p && sbsz[nn]*2ll>within) return gc(nn,x);
seen[x]=1; return x;
}
gp_hash_table<int,int> rol, loc;
void pdfs(int x, int p, int dist, int len) {
assert(!seen[x]);
if(dist > K) return;
if(loc.find(dist) == loc.end()) loc[dist] = len; else loc[dist] = min(loc[dist], len);
for(auto it : tr[x]) if(!seen[nn] && nn != p) {
pdfs(nn, x, dist + it.first, len+1ll);
}
}
void de(int x){
within = gsb(x,-1);
int cen = gc(x,-1);
rol.clear(); loc.clear();
for(auto it : tr[cen]) if(!seen[nn]) {
loc.clear();
pdfs(nn, cen, it.first, 1ll);
for(auto en : loc) {
if(K-en.first < 0) continue;
if(rol.find(K-en.first) != rol.end()) res = min(res, en.second+rol[K-en.first]);
}
for(auto en : loc) { if(en.first < 0 || en.first > K) continue; if(rol.find(en.first) == rol.end()) rol[en.first] = en.second; else rol[en.first] = min(rol[en.first], en.second); }
}
for(auto it : tr[cen]) if(!seen[nn]) {
de(nn);
}
}
signed best_path(signed n, signed k, signed h[][2], signed l[]) {
N = n, K = k;
for(int i = 0; i < N-1; i++) {
int a = h[i][0], b = h[i][1], w = l[i];
tr[a].push_back({w,b});
tr[b].push_back({w,a});
}
de(0);
if(res == LLONG_MAX) return -1; else return res;
}
