//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,sse3,sse4,popcnt,abm,mmx")
#include "race.h"
#include <iostream>
#include <algorithm>
#include <vector>
#include <cmath>
#include <set>
#include <map>
#include <iomanip>
#include <cassert>
#include <stack>
#include <queue>
#include <deque>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>-
using namespace std;
//using namespace __gnu_pbds;
typedef long long ll;
//#define int ll
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
// template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// order_of_key (k) : Number of items strictly smaller than k .
// find_by_order(k) : K-th element in a set (counting from zero).
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define pb push_back
#define ppb pop_back
#define mkp make_pair
#define F first
#define S second
#define lb lower_bound
#define ub upper_bound
#define show(a) cerr << #a <<" -> "<< a <<" "
#define nl cerr <<"\n"
const int MAXN = 2e5 + 5;
const int oo = 1e18 + 5;
int n, k, h[MAXN][2], l[MAXN];
vector <pii> g[MAXN];
int sz[MAXN], ANS = oo;
bool del[MAXN];
set <pii> st;
void calcSZ(int v, int pr = -1) {
sz[v] = 1;
for (pii x : g[v]) {
int to = x.F;
if (to == pr || del[to]) { continue; }
calcSZ(to, v);
sz[v] += sz[to];
}
}
int findCentroid(int v, int pr = -1) {
for (pii x : g[v]) {
int to = x.F;
if (to == pr || del[to]) { continue; }
if (sz[to] > sz[v] / 2) {
sz[v] -= sz[to];
sz[to] += sz[v];
return findCentroid(to, v);
}
}
return v;
}
void update(int v, int pr, int lvl, int d) {
st.insert({d, lvl});
for (pii x : g[v]) {
int to = x.F, w = x.S;
if (to == pr || del[to]) { continue; }
update(to, v, lvl + 1, d + w);
}
}
void query(int v, int pr, int lvl, int d) {
auto it = st.lower_bound({k - d, 0ll});
if (it != st.end()) {
int d2 = it -> F, lvl2 = it -> S;
if (d + d2 == k) {
ANS = min(ANS, lvl + lvl2);
}
}
for (pii x : g[v]) {
int to = x.F, w = x.S;
if (to == pr || del[to]) { continue; }
query(to, v, lvl + 1, d + w);
}
}
void travel(int root) {
calcSZ(root);
int c = findCentroid(root);
st.insert({0, 0});
for (pii x : g[c]) {
int to = x.F, w = x.S;
if (del[to]) { continue; }
query(to, c, 1, w);
update(to, c, 1, w);
}
st.clear();
del[c] = 1;
for (pii x : g[c]) {
int to = x.F;
if (del[to]) { continue; }
travel(to);
}
}
int best_path(int N, int K, int H[][2], int L[]) {
n = N, k = K;
for (int i = 0; i < n-1; ++i) {
h[i][0] = H[i][0];
h[i][1] = H[i][1];
}
for (int i = 0; i < n-1; ++i) {
l[i] = L[i];
int a = h[i][0], b = h[i][1], w = l[i];
g[a].pb({b, w});
g[b].pb({a, w});
}
travel(0);
if (ANS == oo) { return -1; }
return ANS;
}
