// source: https://oj.uz/problem/view/IOI11_race
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
const int mxN = 200000;
const int INF = 1e9;
int n, k, ans;
vector<pair<int, int>> adj[mxN];
map<int, int> paths[mxN];
pair<int, int> offset[mxN];
void upd(map<int, int>& m, int x, int y) {
auto it = m.find(x);
if (it == m.end())
m[x] = y;
else if (y < it->second)
it->second = y;
}
int qry(int u, int x) {
auto it = paths[u].find(x);
return it == paths[u].end() ? INF : it->second + offset[u].second;
}
void dfs(int u = 0, int p = -1) {
upd(paths[u], 0, 0);
for (pair<int, int> v : adj[u]) {
if (v.first == p)
continue;
dfs(v.first, u);
offset[v.first].first += v.second;
++offset[v.first].second;
if (paths[v.first].size() > paths[u].size()) {
swap(paths[u], paths[v.first]);
swap(offset[u], offset[v.first]);
}
for (auto& x : paths[v.first]) {
pair<int, int> real = {x.first + offset[v.first].first, x.second + offset[v.first].second};
if (real.first > k)
continue;
ans = min(ans, real.second + qry(u, k - real.first - offset[u].first));
}
for (auto& x : paths[v.first]) {
pair<int, int> real = {x.first + offset[v.first].first, x.second + offset[v.first].second};
if (real.first > k)
continue;
upd(paths[u], real.first - offset[u].first, real.second - offset[u].second);
}
map<int, int>().swap(paths[v.first]);
}
}
int best_path(int _n, int _k, int h[][2], int l[]) {
n = _n, k = _k, ans = INF;
for (int i = 0; i < n - 1; ++i) {
int u = h[i][0], v = h[i][1], w = l[i];
adj[u].emplace_back(v, w);
adj[v].emplace_back(u, w);
}
dfs();
return ans == INF ? -1 : ans;
}
/*
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n, k; cin >> n >> k;
int h[n - 1][2];
int l[n - 1];
for (int i = 0; i < n - 1; ++i) {
cin >> h[i][0] >> h[i][1];
}
for (int i = 0; i < n - 1; ++i) {
cin >> l[i];
}
cout << best_path(n, k, h, l);
return 0;
}
*/
