#include "race.h"
#include <iostream>
#include <bits/stdc++.h>
#define ll long long
using namespace std;
const ll maxn = 2*1e5+5, INF = 4e18+9;
struct Tree{
int n, root;
vector<int> depth, head, sz, pa;
vector<int> f;
Tree(int n, int root, vector<vector<int>> &adj): n(n), root(root){
depth.resize(n+1, -1);
head.resize(n+1);
sz.resize(n+1, 0);
pa.resize(n+1, -1);
auto rootTree = [&](auto rootTree, int u, int p) -> void{
depth[u] = depth[p]+1;
pa[u] = p;
sz[u] = 1;
for(int v : adj[u]){
if(v == p) continue;
rootTree(rootTree, v, u);
sz[u] += sz[v];
}
};
rootTree(rootTree, root, 0);
auto decompose = [&](auto decompose, int u, int h) -> void{
head[u] = h;
int heavy = -1;
for(int v : adj[u]){
if(v == pa[u]) continue;
if(heavy == -1 || sz[heavy] < sz[v]) heavy = v;
}
if(heavy != -1) decompose(decompose, heavy, h);
for(int v : adj[u]){
if(v == pa[u] || v == heavy) continue;
decompose(decompose, v, v);
}
};
decompose(decompose, root, root);
f = [&]{
vector<array<int, 2>> first(n+1);
vector<array<int, 2>> second(n+1);
function<void(int, int)> dfs0 = [&](int u, int p) {
first[u] = second[u] = {0, -1};
for (int v : adj[u]) {
if (v == p) {
continue;
}
dfs0(v, u);
auto fetch = first[v];
fetch[0] += 1;
fetch[1] = v;
if (fetch > first[u]) {
swap(fetch, first[u]);
}
if (fetch > second[u]) {
swap(fetch, second[u]);
}
}
};
dfs0(1, 0);
function<void(int, int)> dfs = [&](int u, int p) {
for (int v : adj[u]) {
if (v == p) {
continue;
}
auto fetch = first[u][1] == v ? second[u] : first[u];
fetch[0] += 1;
fetch[1] = u;
if (fetch > first[v]) {
swap(fetch, first[v]);
}
if (fetch > second[v]) {
swap(fetch, second[v]);
}
dfs(v, u);
}
};
dfs(1, 0);
vector<int> f(n+1);
for (int u = 1; u <= n; u++) {
f[u] = first[u][0];
}
return f;
}();
};
int lca(int u, int v){
for(; head[u] != head[v]; v = pa[head[v]]){
if(depth[head[u]] > depth[head[v]]) swap(u, v);
}
if(depth[u] > depth[v]) swap(u, v);
return u;
}
int dist(int u, int v) {
return depth[u]+depth[v]-2*depth[lca(u, v)];
}
};
int best_path(int N, int K, int H[][2], int L[])
{
int n = N;
vector<vector<pair<ll, ll>>> adj(n+1);
for(int i = 0; i < n-1; i++){
int u = H[i][0], v = H[i][1];
u++; v++;
adj[u].push_back({v, L[i]});
adj[v].push_back({u, L[i]});
}
vector<int> pa(n+1), depth(n+1, 0);
depth[0] = -1;
vector<ll> path(n+1);
auto rtree = [&](auto rtree, int u, int p, ll len) -> void{
path[u] = len;
depth[u] = depth[p]+1;
pa[u] = p;
for(auto it : adj[u]){
int v = it.first, w = it.second;
if(v == p) continue;
rtree(rtree, v, u, len+w);
}
};
rtree(rtree, 1, 0, 0);
vector<map<ll, ll>> mp(n+1);
ll ans = INF;
auto dfs = [&](auto dfs, int u, int p) -> void{
mp[u][path[u]] = depth[u];
for(auto it : adj[u]){
int v = it.first;
if(v == p) continue;
dfs(dfs, v, u);
if(mp[u].size() < mp[v].size()) swap(mp[u], mp[v]);
for(auto it : mp[v]){
if(mp[u].count(K+2*path[u]-it.first)){
ans = min(ans, mp[u][K+2*path[u]-it.first]+it.second-2*depth[u]);
}
}
for(auto it : mp[v]){
if(mp[u].count(it.first)){
mp[u][it.first] = min(mp[u][it.first], it.second);
}else{
mp[u][it.first] = it.second;
}
}
}
if(mp[u].count(K+path[u])){
ans = min(ans, mp[u][K+path[u]]-depth[u]);
}
};
dfs(dfs, 1, 0);
if(ans == INF) ans = -1;
return ans;
}
