#include <bits/stdc++.h>
using namespace std;
#define s second
#define f first
#define pb push_back
typedef long long ll;
typedef pair<ll, ll> pii;
typedef vector<pii> vpii;
typedef vector<ll> vi;
#define FOR(i, a, b) for (ll i = (a); i<b; i++)
const ll MN = 3e5 + 10;
vpii adj[MN];
ll d[MN]; // from root in highways
ll d2[MN]; // from root in distance
ll k;
map<ll, ll> small[MN];
void dfs(ll cur = 0, ll dist = 0, ll dist2 = 0, ll p = -1) {
// cout << cur << endl;
d[cur]=dist;
d2[cur]=dist2;
small[cur][dist2]=dist;
for (auto val: adj[cur]) {
if (val.f != p) {
dfs(val.f, dist + 1ll, dist2 + val.s, cur);
}
}
}
ll ans = 1e9;
void solve(ll cur, ll p=-1) {
ll target = k + 2*d2[cur];
for (auto val: adj[cur]) {
if (val.f != p) {
solve(val.f, cur);
if (small[val.f].size() > small[cur].size()) swap(small[val.f], small[cur]);
for (pii nx: small[val.f]) {
if (small[cur].find(target - nx.f) != small[cur].end()) {
ans = min(ans, small[cur][target - nx.f] + nx.s - 2*d[cur]);
}
}
for (pii nx: small[val.f]) {
if (small[cur].find(nx.f) == small[cur].end()) small[cur].insert(nx);
else small[cur][nx.f]=min(small[cur][nx.f], nx.s);
}
}
}
}
int best_path(int N, int K, int H[][2], int L[])
{
k = K;
FOR(i, 0, N-1) {
adj[H[i][0]].pb({H[i][1], L[i]});
adj[H[i][1]].pb({H[i][0], L[i]});
}
dfs();
solve(0);
if (ans == 1e9) ans = -1;
return ans;
}
