#include <bits/stdc++.h>
using namespace std;
vector<vector<pair<size_t, int>>> graph;
const int oo = INT_MAX / 3;
int& rd(map<int, int>& m, int key)
{
auto it = m.find(key);
if(it == m.end()) it = m.emplace_hint(it, key, +oo);
return it->second;
}
void mini(map<int, int>& m, int key, int value)
{
rd(m, key) = min(rd(m, key), value);
}
void dfs_map_paths(size_t u, int s, int d, map<int, int>& m,
size_t glock = SIZE_MAX, size_t lock = SIZE_MAX)
{
if(d > +oo) return;
mini(m, s, d);
for(auto [v, w] : graph[u])
if(v != lock and v != glock)
dfs_map_paths(v, s + w, d + 1, m, glock, u);
}
int best_path(int _n, int k, int H[][2], int L[])
{
const size_t n = _n;
graph.resize(n);
for(size_t i = 0; i < n - 1; i++)
{
graph[H[i][0]].emplace_back(H[i][1], L[i]);
graph[H[i][1]].emplace_back(H[i][0], L[i]);
}
int result = +oo;
for(size_t f = 0; f < n; f++)
{
map<int, int> pre = {{0, 0}};
for(auto [v, w] : graph[f])
{
map<int, int> cur;
dfs_map_paths(v, w, 1, cur);
for(auto [s, d] : cur)
result = min(result, d + rd(pre, k - s));
for(auto [s, d] : cur)
mini(pre, s, d);
}
}
return result;
}
