#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
const int MAXN = 1e6+10, inf = 1e6+3;
int n, k, mn[MAXN], ans = inf, all, sz[MAXN], par[MAXN], h[MAXN];
vector <pair<int,int>> adj[MAXN];
vector <int> clr;
ll d[MAXN];
bool dead[MAXN];
void dfs(int v, int parv){
all++; sz[v] = 1;
for(auto u: adj[v]){
if(!dead[u.first] && u.first != parv){
par[u.first] = v;
dfs(u.first, v);
sz[v] += sz[u.first];
}
}
return;
}
inline int findcentroid(int v){
all = 0;
int cent = v; par[v] = -1;
dfs(v, -1);
bool f = false;
while(!f){
f = true;
for(auto u: adj[cent]){
if(!dead[u.first] && u.first != par[cent] && sz[u.first] >= (all / 2)){
f = false;
cent = u.first;
break;
}
}
}
return cent;
}
void see(int v, int parv){
if(d[v]<=k) ans = min(ans, h[v]+mn[k-d[v]]);
for(auto i: adj[v]){
int u = i.first, w = i.second;
if(dead[u] || u==parv) continue;
h[u] = h[v]+1; d[u] = d[v]+(ll)w;
see(u, v);
}
return;
}
void add(int v, int parv){
if(d[v]<k){
mn[d[v]] = min(mn[d[v]], h[v]);
clr.push_back(d[v]);
}
for(auto i: adj[v]){
int u = i.first;
if(dead[u] || u == parv) continue;
add(u,v);
}
return;
}
inline void calc(int r){
mn[0] = 0; h[r] = 0; d[r] = 0; clr.push_back(0);
for(auto i: adj[r]){
int u = i.first;
if(dead[u]) continue;
h[u] = 1; d[u] = (ll)i.second;
see(u, r);
add(u, r);
}
while(!clr.empty()){
mn[clr.back()] = inf; clr.pop_back();
}
return;
}
void slv(int v, int tt = 0){
int cent = findcentroid(v);
calc(cent);
dead[cent] = true;
for(auto u: adj[cent])
if(!dead[u.first]) slv(u.first, tt+1);
return;
}
int best_path(int N, int K, int H[][2], int L[]){
n = N; k = K;
for(int i = 0; i < n-1; i++){
adj[H[i][0]].push_back({H[i][1], L[i]});
adj[H[i][1]].push_back({H[i][0], L[i]});
}
for(int i = 0; i < MAXN; i++) mn[i] = inf;
slv(0);
return (ans>=inf?-1:ans);
}
/*int main()
{
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin >> n >> k;
for(int i = 0; i < n-1; i++){
int u,v,w;
cin >> u >> v >> w;
adj[u].push_back({v,w});
adj[v].push_back({u,w});
}
for(int i = 0; i < MAXN; i++) mn[i] = inf;
slv(0);
cout << (ans>=inf?-1:ans) << endl;
return 0;
}*/
