#include <bits/stdc++.h>
using namespace std;
const int N = 1<<18, INF = 1e9;
int k, x, y, ans = INF, dp[1<<20], sub[N];
array<int,2> a[N];
array<int,4> d[N];
vector<array<int,2>> e[N];
bitset<N> b;
void subDfs(int c, int p)
{
sub[c]=1;
for (auto i : e[c])
if (i[0]!=p&&!b[i[0]])
{
subDfs(i[0],c);
sub[c]+=sub[i[0]];
}
}
int findC(int c, int p, int t)
{
for (auto i : e[c])
if (i[0]!=p&&!b[i[0]]&&sub[i[0]]>t)
return findC(i[0],c,t);
return c;
}
void dfs(int c, int p, int h, int t)
{
a[x++]={h,t};
ans=min(ans,dp[k-h]+t);
for (auto i : e[c])
if (i[0]!=p&&h+i[1]<=k)
dfs(i[0],c,h+i[1],t+1);
}
void solve(int n)
{
subDfs(n,-1);
int c = findC(n,-1,sub[n]/2);
b[c]=1;
x=0;
for (auto i : e[c])
if (!b[i[0]]&&i[1]<=k)
{
y=x;
dfs(i[0],c,i[1],1);
for (int j=y;j<x;++j)
dp[a[j][0]]=min(dp[a[j][0]],a[j][1]);
}
for (int i=0;i<x;++i)
dp[a[i][0]]=INF;
for (auto i : e[c])
if (!b[i[0]])
solve(i[0]);
}
int best_path(int n, int K, int h[][2], int l[])
{
k=K;
for (int i=0;i<n-1;++i)
{
e[h[i][0]].push_back({h[i][1],l[i]});
e[h[i][1]].push_back({h[i][0],l[i]});
}
for (int i=1;i<=k;++i)
dp[i]=INF;
solve(0);
if (ans==INF)
return -1;
return ans;
}
