#include <bits/stdc++.h>
#define foreach for
#define in :
using namespace std;
typedef long long ll;
/*
Konichiwa
Konichiwa
Ara ~~ ara
Bob no taisuki - Shinobu Kocho
* * * * *
* *
* *
* * I love SHINOBU <3 <3 <3
* *
* *
* * * * *
*/
/*
_________________________
Author : Bob15324
_________________________
*/
template<class X , class Y>
bool Minimize(X & x , Y y)
{
if( x == -1 || (x >y && y > 0))
{
x = y;
return true;
}
return false;
}
template<class X , class Y>
bool Maximize(X & x , Y y)
{
if( x < y)
{
x = y;
return true;
}
return false;
}
/* End of templates. Let's see what do we have here */
const int N = 2e5+1;
int res = -1;
class GRAPH
{
private:
vector<set<pair<int ,int >>>vertices;
vector<int>sub_size;
vector<map<int ,int >>dict;
public:
GRAPH(int _n)
{
vertices.resize(_n+1);
sub_size.resize(_n+1);
dict.resize(_n+1);
}
void AddEdge(int u ,int v ,int w)
{
vertices[u].insert(make_pair(v , w));
vertices[v].insert(make_pair(u , w));
}
int DFS(int u ,int daddy)
{
sub_size[u] = 1;
foreach(pair<int ,int > adj in vertices[u])
{
int v = adj.first;
if(v == daddy)
{
continue;
}
sub_size[u] += DFS(v , u);
}
return sub_size[u];
}
int centroid(int u ,int daddy , int lim)
{
foreach(pair<int ,int > adj in vertices[u])
{
int v = adj.first;
if(v == daddy)
{
continue;
}
if(sub_size[v] > lim)
{
return centroid(v , u , lim);
}
}
return u;
}
void dfs2(int u ,int daddy ,int base , int distance , int s ,int k)
{
if(dict[base].count(s))
{
Minimize(dict[base][s], distance );
}else
{
dict[base][s] = distance;
}
foreach(pair<int , int >adj in vertices[u])
{
int v = adj.first;
if ( v== daddy)
{
continue;
}
if(s + adj.second > k)
{
continue;
}
dfs2(v , u , base , distance + 1 , s + adj.second , k);
}
}
void Build(int u, int daddy ,int k )
{
int lim = DFS(u , daddy);
int _c = centroid(u , daddy , lim >> 1);
dfs2(_c , daddy , _c , 0 , 0 , k);
dict[_c][0] = 0;
foreach(auto val in dict[_c])
{
if(dict[_c].count(k - val.first))
{
Minimize(res , dict[_c][k-val.first] + val.second);
}
}
set<pair<int ,int >> temp = vertices[_c];
foreach(pair<int ,int > adj in temp )
{
vertices[_c].erase(adj);
vertices[adj.first].erase(make_pair(_c , adj.second));
Build(adj.first , _c , k);
}
}
};
int best_path(int n , int m ,int H[][2] , int L[])
{
GRAPH graph(n);
for(int i = 0 ; i < n -1 ; i++)
{
H[i][0]++;
H[i][1]++;
graph.AddEdge(H[i][0] , H[i][1] , L[i]);
}
graph.Build(1 , - 1 , m);
return res;
}
//Ehem. My code is amazing. Pay me 2$.Thank you.
