#include "race.h"
#include "bits/stdc++.h"
using namespace std;
using ll = long long;
const int MAXN = 2e5+5;
vector< vector< pair<ll, int> > > adj(MAXN);
ll ans = 1e9;
int sz[MAXN];
int par_cent[MAXN];
pair<ll, ll> len[MAXN];
bool visited[MAXN];
int k;
//int cent;
void dfs_len(int v, int p, pair<ll, ll> prev)
{
for(pair<ll, int> e : adj[v])
{
if(e.second == p || visited[e.second])
continue;
len[e.second].first = prev.first + e.first;
len[e.second].second = prev.second + 1;
dfs_len(e.second, v, len[e.second]);
}
}
int dfs_sz(int v, int p)
{
sz[v] = 1;
for(pair<ll, int> e : adj[v])
{
if(e.second == p || visited[e.second])
continue;
int tmp = dfs_sz(e.second, v);
sz[v] += tmp;
}
return sz[v];
}
int dfs_cent(int v, int p, int n)
{
//cout << v << "\n";
for(pair<ll, int> e : adj[v])
{
if(e.second == p || visited[e.second])
continue;
if(sz[e.second] * 2 > n)
return dfs_cent(e.second, v, n);
}
return v;
}
pair<multiset<pair<ll, int> >, int > centroid(int v, int p)
{
int n = dfs_sz(v, p);
int cent = dfs_cent(v, p, n);
visited[cent] = true;
par_cent[cent] = p;
multiset< pair<ll, int> > curr;
curr.insert({0, 0});
vector< pair<multiset<pair<ll, int> >, int> > allvals;
dfs_len(cent, p, {0, 0});
for(pair<ll, int> e : adj[cent])
{
if(e.second != p && !visited[e.second]) {
pair<multiset<pair<ll, int> >, int> temp = centroid(e.second, cent);
allvals.push_back(temp);
}
}
for(pair<multiset<pair<ll, int> >, int> tmp : allvals)
{
for(pair<ll, int> l : tmp.first)
{
ll needed = k - l.first - len[tmp.second].first;
auto it = curr.lower_bound({needed, 0});
if(it == curr.end() || (*it).first != needed)
continue;
ans = min(ans, (*it).second + l.second + len[tmp.second].second);
//if(ans == (*it).second + l.second + len[tmp.second].second)
//cout << ans << " " << v << " " << tmp.second << " " << len[tmp.second].second << "\n";
}
for(pair<ll, int> l : tmp.first)
curr.insert({l.first + len[tmp.second].first, l.second + len[tmp.second].second});
}
return {curr, cent};
}
int best_path(int N, int K, int H[][2], int L[])
{
k = K;
for(int i = 0; i < N - 1; i++)
{
adj[H[i][0]].push_back({L[i], H[i][1]});
adj[H[i][1]].push_back({L[i], H[i][0]});
}
centroid(0, -1);
if(ans == 1e9)
ans = -1;
return ans;
}
