#include<iostream>
#include<vector>
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
using namespace std;
vector< pii > adj[200005];
bool rem[200005];
int K, sub[200005], par[200005], nxt;
int arr[1000005], best=1e9, ans=1e9, inf=1e9;
vector< pii > q;
void dfs1(int u)
{
sub[u]=1;
for(pii v: adj[u])
{
if(v.first!=par[u] && !rem[v.first])
{
par[v.first]=u;
dfs1(v.first);
sub[u]+=sub[v.first];
}
}
}
void dfs2(int u, int cand)
{
int currsz=sub[cand]-sub[u];
for(pii v: adj[u])
{
if(v.first!=par[u] && !rem[v.first])
{
currsz=max(currsz, sub[v.first]);
dfs2(v.first, cand);
}
}
if(currsz<best)
{
nxt=u;
best=currsz;
}
}
void dfs3(int u, int w, int l)
{
if(w>K) return;
q.pb(mp(w, l));
for(pii v: adj[u])
{
if(v.first!=par[u] && !rem[v.first])
{
par[v.first]=u;
dfs3(v.first, w+v.second, l+1);
}
}
}
void solve(int cent)
{
vector<int> tnow;
tnow.pb(0);
arr[0]=0;
for(pii v: adj[cent])
{
if(!rem[v.first])
{
par[v.first]=cent;
dfs3(v.first, v.second, 1);
}
for(int i = 0; i < q.size(); i++)
{
int w=q[i].first, l=q[i].second;
if(w<=K)
ans=min(ans, arr[K-w]+l);
}
for(int i = 0; i < q.size(); i++)
{
arr[q[i].first]=min(arr[q[i].first], q[i].second);
tnow.pb(q[i].first);
}
q.clear();
}
for(int i = 0; i < tnow.size(); i++)
arr[tnow[i]]=inf;
tnow.clear();
}
void cent(int cand)
{
nxt=0;
best=inf;
par[cand]=cand;
dfs1(cand);
dfs2(cand, cand);
solve(nxt);
rem[nxt]=true;
for(pii v: adj[nxt])
if(!rem[v.first])
cent(v.first);
}
int best_path(int n, int k, int h[][2], int l[])
{
K=k;
for(int i = 1; i <= n; i++)
{
adj[i].clear();
rem[i]=false;
}
for(int i = 0; i <= k; i++)
arr[i]=inf;
for(int i = 0; i < n-1; i++)
{
adj[h[i][0]].pb(mp(h[i][1], l[i]));
adj[h[i][1]].pb(mp(h[i][0], l[i]));
}
cent(1);
if(ans==inf) ans=-1;
return ans;
}
/*int main()
{
int arr[][2]={{0, 1}, {1, 2}};
int lnt[]={1, 1};
cout << best_path(11, 12, arr, lnt);
}*/
