#include <bits/stdc++.h>
// #include "race.h"
// #include <ext/pb_ds/assoc_container.hpp>
// using namespace __gnu_pbds;
// #pragma GCC optimize ("Ofast")
// #pragma GCC target ("avx,avx2")
using namespace std;
typedef long long ll;
typedef pair<ll, int> pp;
#define rep(i,l,r) for(int i = (l); i < r; i++)
#define per(i,r,l) for(int i = (r); i >= l; i--)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
#define pb push_back
#define ff first
#define ss second
const ll mod = 998244353, maxn = 1e6 + 5, inf = 1e9 + 5;
bool ban[maxn];
int cnt[maxn], k;
vector<pp> adj[maxn], st[maxn];
int dist[maxn];
void set_cnt(int r, int p){
cnt[r] = 1;
for(pp c: adj[r]) if(c.ff != p && !ban[c.ff]){
set_cnt(c.ff, r);
cnt[r] += cnt[c.ff];
}
}
int findCenteroid(int r, int p, int tot){
for(pp c: adj[r]) if(c.ff != p && !ban[c.ff]){
if(cnt[c.ff] >= tot - cnt[c.ff]) return findCenteroid(c.ff, r, tot);
}
return r;
}
void dfs(int r, int p, int rt, ll len, int w){
st[rt].pb({len, w});
for(pp c: adj[r]) if(c.ff != p && !ban[c.ff]) dfs(c.ff, r, rt, len + c.ss, w + 1);
}
int slv(int r){
set_cnt(r, r);
r = findCenteroid(r, r, cnt[r]);
int ans = inf;
for(pp c: adj[r]) if(!ban[c.ff]){
dfs(c.ff, r, c.ff, c.ss, 1);
for(pp t: st[c.ff]){
int v = k - t.ff;
if(v < 0 || (v > 0 && dist[v] == 0)) continue;
ans = min(ans, dist[v] + t.ss);
}
for(pp t: st[c.ff]){
if(t.ff > k) continue;
if(dist[t.ff] == 0) dist[t.ff] = t.ss;
dist[t.ff] = min(dist[t.ff], t.ss);
}
}
for(pp c: adj[r]) if(!ban[c.ff]){
for(pp t: st[c.ff]){
if(t.ff > k) continue;
dist[t.ff] = 0;
}
st[c.ff].clear();
}
ban[r] = true;
for(pp c: adj[r]) if(!ban[c.ff]){
ans = min(ans, slv(c.ff));
}
return ans;
}
int best_path(int N, int K, int H[][2], int L[]){
k = K;
rep(i,0,N-1){
adj[H[i][0]].pb({H[i][1], L[i]});
adj[H[i][1]].pb({H[i][0], L[i]});
}
int ans = slv(0);
return ans == inf? -1: ans;
}
