//
// main.cpp
// fireworks
//
// Created by Trần Nam Khánh on 11/21/20.
//
#include <iostream>
#include <queue>
using namespace std;
const long long nax=3e5+1;
struct data
{
long long a,b,p,c;
priority_queue<long long>*q;
data operator +(data tmp)
{
data s;
s.p=p;
s.c=c;
s.a=a+tmp.a;
s.b=b+tmp.b;
if(q->size()<tmp.q->size())swap(q,tmp.q);
s.q=q;
while(!tmp.q->empty())
{
s.q->push(tmp.q->top());
tmp.q->pop();
}
return s;
}
}d[nax];
long long n,m;
int main() {
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>n>>m;
for(long long i=2;i<=n+m;i++)
{
cin>>d[i].p>>d[i].c;
}
for(long long i=1;i<=n+m;i++)
{
d[i].a=0;
d[i].b=0;
d[i].q=new priority_queue<long long>;
}
for(long long i=n+m;i>n;i--)
{
d[i].a=1;
d[i].b=0;
d[i].q->push(0);
d[i].q->push(0);
}
for(long long i=n+m;i>=2;i--)
{
long long p=d[i].p;
while(d[i].a>1)
{
d[i].a--;
d[i].b+=d[i].q->top();
d[i].q->pop();
}
d[i].b-=d[i].c;
long long t1=d[i].q->top();d[i].q->pop();
long long t0=d[i].q->top();d[i].q->pop();
d[i].q->push(t0+d[i].c);
d[i].q->push(t1+d[i].c);
d[p]=d[p]+d[i];
}
while(d[1].a>0)
{
d[1].a--;
d[1].b+=d[1].q->top();
d[1].q->pop();
}
cout<<d[1].b<<endl;
return 0;
}
/*
4 6
1 5
2 5
2 8
3 3
3 2
3 3
2 9
4 4
4 3
*/
