#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
const int mxN = 2e5 + 5, inf = 1e9;
int sz[mxN], cenPar[mxN], dep[mxN], par[mxN][18], sum[mxN], cnt = 0;
vector<int> first(mxN, -1);
vector<array<int, 2>> adj[mxN], euler;
vector<array<int, 3>> dists[mxN];
bool done[mxN];
void dfs(int u, int p){
if(first[u] == -1){
first[u] = cnt++;
}
euler.push_back({dep[u], u});
for(auto i : adj[u]){
if(i[0] == p) continue;
dep[i[0]] = dep[u] + 1;
sum[i[0]] = sum[u] + i[1];
dfs(i[0], u);
euler.push_back({dep[u], u});
}
}
array<int, 2> table[2 * mxN][20];
int lg[2 * mxN];
void initTable(){
for(int i = 2; i < 2 * mxN; i++){
lg[i] = lg[i / 2] + 1;
}
int sz = euler.size();
for(int i = 0; i < sz; i++){
table[i][0] = euler[i];
}
for(int j = 1; j < 20; j++) {
for(int i = 0; i + (1 << j) <= sz; i++) {
table[i][j] = min(table[i][j-1], table[i + (1 << (j-1))][j-1]);
}
}
}
int lca(int a, int b){
a = first[a];
b = first[b];
if(a > b) swap(a, b);
int j = lg[b + 1 - a];
return min(table[a][j], table[b + 1 - (1<<j)][j])[1];
}
int calcDist(int a, int b){
return sum[a] + sum[b] - 2 * sum[lca(a, b)];
}
int calcSz(int u, int p){
sz[u] = 1;
for(auto i : adj[u]){
if(i[0] == p || done[i[0]]) continue;
sz[u] += calcSz(i[0], u);
}
return sz[u];
}
int get(int u, int p, int x){
for(auto i : adj[u]){
if(i[0] == p || done[i[0]]) continue;
if(sz[i[0]] * 2 > x){
return get(i[0], u, x);
}
}
return u;
}
int build(int u){
int centroid = get(u, u, calcSz(u, u));
done[centroid] = 1;
dists[centroid].push_back({0, centroid, centroid});
for(auto i : adj[centroid]){
if(!done[i[0]]){
int x = build(i[0]);
cenPar[x] = centroid;
for(auto j : dists[x]){
dists[centroid].push_back({calcDist(centroid, j[2]), x, j[2]});
}
}
}
sort(dists[centroid].begin(), dists[centroid].end());
return centroid;
}
int qry(int v, int k){
int cur = v, subtree = v;
int ans = inf;
while(cur != -1){
int goal = k - calcDist(v, cur);
array<int, 3> find = {goal, -inf, -inf};
int lb = lower_bound(dists[cur].begin(), dists[cur].end(), find) - dists[cur].begin();
for(int j = lb; j < dists[cur].size() && dists[cur][j][0] == goal; j++){
if(dists[cur][j][1] == subtree) continue;
int x = dep[v] + dep[cur] - 2 * dep[lca(cur, v)];
int y = dep[dists[cur][j][2]] + dep[cur] - 2 * dep[lca(dists[cur][j][2], cur)];
ans = min(ans, x + y);
//cout << v << " " << dists[cur][j][2] << ' ' << x + y << '\n';
}
subtree = cur;
cur = cenPar[cur];
}
return ans;
}
int best_path(int n, int k, int h[][2], int l[]){
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]});
}
dfs(0, 0);
initTable();
for(int i = 0; i < n; i++){
cenPar[i] = -1;
}
build(0);
/*for(int i = 0; i < n; i++){
cout << cenPar[i] << " ";
}
cout << '\n';
for(int i = 0; i < n; i++){
cout << i << '\n';
for(auto j : dists[i]){
cout << j[0] << " " << j[1] << " " << j[2] << "\n";
}
cout << '\n';
}*/
int ans = inf;
for(int i = 0; i < n; i++){
//cout << qry(i, k) << " ";
ans = min(ans, qry(i, k));
}
return (ans == inf ? -1 : ans);
}
