#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define ff first
#define ss second
void steroids() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(0);
}
const int N = 2e5;
const int inf = 1e9;
std::vector<std::pair<int, int>> adj[N];
int h[N][2];
int l[N];
int d[N];
ll dis_from_root[N];
int n, k;
int ans;
std::map<ll, int> paths[N];
void dfs(const int &u, const int &par, const ll &cur_dist, const int &cur_height) {
paths[u][cur_dist] = cur_height;
dis_from_root[u] = cur_dist;
d[u] = cur_height;
for (const auto &p : adj[u]) {
if (p.ff != par){
dfs(p.ff, u, cur_dist + p.ss, cur_height + 1);
}
}
}
void smol_to_larg(const int &u, const int &p) {
ll target = 0LL + k + 2 * dis_from_root[u];
for (const auto &[v, w] : adj[u]) {
if (v != p) {
smol_to_larg(v, u);
if (paths[v].size() > paths[u].size()) paths[u].swap(paths[v]);
for (const auto &[len, dis] : paths[v]) {
if (paths[u].find(target - len) != paths[u].end()) {
ans = std::min(ans, dis + paths[u][target-len] - 2 * d[u]);
}
}
for (const auto &p : paths[v]) {
if (paths[u].find(p.ff) == paths[u].end()) {
paths[u].insert(p);
} else {
paths[u][p.ff] = std::min(paths[u][p.ff], p.ss);
}
}
}
}
}
int best_path(const int &Num, const int &Req, int h[][2], int l[]){
n = Num;
k = Req;
ans = inf;
for (int i = 0; i < n-1; i++) {
adj[h[i][0]].push_back({h[i][1], l[i]});
adj[h[i][1]].push_back({h[i][0], l[i]});
}
d[0] = 0;
dfs(0, -1, 0, 0);
smol_to_larg(0, -1);
return ans == inf ? -1 : ans;
}
/*int main() {
steroids();
int nn, kk;
std::cin >> nn >> kk;
for (int i = 0; i < nn-1; i++) {
std::cin >> h[i][0] >> h[i][1];
}
for (int i = 0; i < nn-1; i++) {
std::cin >> l[i];
}
std::cout << best_path(nn, kk, h, l);
}
*/
