/*If we keep holding onto yesterday, what are we going to be tomorrow?*/
#include<bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
#define F first
#define S second
typedef long long ll;
vector<pair<int,int>>g[N];
int sub[N] , process[N];
int n , k ;
int mp[1000100];
int dfs(int u , int p)
{
sub[u] = 1;
for(auto v : g[u]){
if(v.F != p && !process[v.F]){
sub[u] += dfs(v.F,u);
}
}
return sub[u];
}
int centroid(int u , int p , int req)
{
for(auto v : g[u]){
if(v.F != p && !process[v.F] && sub[v.F] >= req){
return centroid(v.F,u,req);
}
}
return u;
}
int ans = INT_MAX;
void f(int u ,int p , int keep , ll depth , int level)
{
if(depth > k) return;
if(!keep){
ll x = k-depth;
if(mp[x] != -1){
ans = min(ans,mp[x] + level);
}
}
else{
if(mp[depth] == -1){
mp[depth] = level;
}
else mp[depth] = min(mp[depth],level);
}
for(auto v : g[u]){
if(v.F != p && !process[v.F]){
f(v.F,u,keep,depth+v.S,level+1);
}
}
}
void decompose(int u)
{
ll x = dfs(u,-1);
ll cen = centroid(u,0,x/2);
process[cen] = 1;
mp[0] = 0;
for(auto v : g[cen]){
if(!process[v.F]){
f(v.F,cen,0,v.S,1);
f(v.F,cen,1,v.S,1);
}
}
memset(mp,-1,sizeof(mp));
for(auto v : g[cen]){
if(!process[v.F]) decompose(v.F);
}
}
int best_path(int _N, int _K, int H[][2], int L[])
{
memset(mp,-1,sizeof(mp));
for(int i = 0 ; i < _N - 1 ; i ++){
int x = H[i][0] , y = H[i][1] , w = L[i];
g[x].push_back({y,w});
g[y].push_back({x,w});
}
decompose(0);
if(ans == INT_MAX) ans = -1;
return ans;
}
