//#include "race.h"
#include <bits/stdc++.h>
#define fi first
#define se second
using namespace std;
typedef pair<int, int> pii;
const int MX = 200005;
int n, k, ans = MX;
int numC[MX];
bitset<MX> vist;
vector<pii> G[MX];
void calChild(int u, int p){
numC[u] = 1;
for(pii &tmp: G[u]){
int v, c;
tie(v, c) = tmp;
if(v==p || vist[v]) continue;
calChild(v, u);
numC[u] += numC[v];
}
}
int Centroid(int u, int p, const int &half){
for(pii &tmp: G[u]){
int v = tmp.fi;
if(v == p || vist[v]) continue;
if(numC[v] > half) return Centroid(v, u, half);
}
return u;
}
int dis[MX];
int node[MX];
int getmap(map<int, int> &mp, int value){
auto itr = mp.find(value);
if(itr == mp.end()) return 0;
return itr->se;
}
int calValue(int u){
map<int, int> mp;
int res = MX;
mp[0] = 1;
for(pii &tmp: G[u]){
int v, c;
tie(v, c) = tmp;
if (vist[v]) continue;
vector<int> path;
stack<pii> Q;
Q.push({v, u});
node[v] = 2;
dis[v] = c;
while(Q.size()){
int u, p;
tie(u, p) = Q.top();
Q.pop();
path.push_back(u);
for(pii &tmp: G[u]){
int v, c;
tie(v, c) = tmp;
if(vist[v] || v == p) continue;
Q.push({v, u});
dis[v] = dis[u] + c;
node[v] = node[u] + 1;
}
}
for(int vt: path) if(dis[vt]<=k){
int gm = getmap(mp, k - dis[vt]);
if(gm) res = min(res, gm + node[vt] - 1);
}
for(int vt: path) if(dis[vt]<=k){
if(mp[dis[vt]]==0) mp[dis[vt]] = node[vt];
else mp[dis[vt]] = min(mp[dis[vt]], node[vt]);
}
}
return res;
}
void dwuy_simp_nvpu(int u){
calChild(u, 0);
u = Centroid(u, 0, numC[u]>>1);
ans = min(ans, calValue(u));
vist[u] = 1;
for(pii &tmp: G[u]){
int v = tmp.fi;
if(!vist[v]) dwuy_simp_nvpu(v);
}
}
int best_path(int N, int K, int H[][2], int L[]){
n = N;
k = K;
for(int i=0; i<n-1; i++){
int u = H[i][0];
int v = H[i][1];
int c = L[i];
u++, v++;
G[u].push_back({v, c});
G[v].push_back({u, c});
}
dwuy_simp_nvpu(1);
return ans==MX? -1 : ans - 1;
}
