#include <bits/stdc++.h>
#include <race.h>
using namespace std;
#define task ""
const int MAX = 200000;
int n, k;
int h[MAX];
long long dep[MAX];
int sz[MAX], heavy[MAX];
vector<pair<int, int>> adj[MAX];
void dfsSZ(int u, int p) {
sz[u] = 1; heavy[u] = -1;
for (pair<int, int> &e: adj[u]) if (e.first != p) {
int v = e.first, w = e.second;
dep[v] = dep[u] + w;
h[v] = h[u] + 1;
dfsSZ(v, u);
sz[u] += sz[v];
if (heavy[u] == -1 || sz[heavy[u]] < sz[v]) heavy[u] = v;
}
}
multiset<pair<long long, int>> dp; int res;
vector<int> node;
void upd(int u, int p, int lca) {
if (lca == -1) dp.erase(dp.find(make_pair(dep[u], h[u])));
else {
long long value = k - dep[u] + 2LL * dep[lca];
auto it = dp.lower_bound(make_pair(value, 0));
if (it != dp.end() && (*it).first == value) {
res = min(res,
h[u] + (*it).second - 2 * h[lca]);
}
node.push_back(u);
}
for (pair<int, int> &e: adj[u]) if (e.first != p) {
upd(e.first, u, lca);
}
}
void dfs(int u, int p) {
for (pair<int, int> &e: adj[u]) if (e.first != p && e.first != heavy[u]) {
dfs(e.first, u);
upd(e.first, u, -1);
}
if (heavy[u] > -1) {
dfs(heavy[u], u);
for (pair<int, int> &e: adj[u]) if (e.first != p && e.first != heavy[u]) {
upd(e.first, u, u);
while (node.size()) {
int uu = node.back(); node.pop_back();
dp.insert(make_pair(dep[uu], h[uu]));
}
}
}
long long value = dep[u] + k;
auto it = dp.lower_bound(make_pair(value, 0));
if (it != dp.end() && (*it).first == value) {
res = min(res, (*it).second - h[u]);
}
dp.insert(make_pair(dep[u], h[u]));
}
int best_path(int N, int K, int H[][2], int L[]) {
res = N;
n = N;
k = K;
for (int i = 0; i < N - 1; ++i) {
adj[H[i][0]].push_back(make_pair(H[i][1], L[i]));
adj[H[i][1]].push_back(make_pair(H[i][0], L[i]));
}
dfsSZ(0, -1);
dfs(0, -1);
return res == n ? -1 : res;
}
