#include <bits/stdc++.h>
#define int long long
using namespace std;
const int nmax = 3e5;
int n, m;
int t[nmax + 5], c[nmax + 5];
vector<int> G[nmax + 5];
struct funct
{
int a, b;
priority_queue<int> *h;
funct()
{
a = b = 0;
h = new priority_queue<int>;
}
void operator += (funct other)
{
a += other.a;
b += other.b;
if(other.h->size() > h->size())
{
swap(other.h, h);
}
while(!other.h->empty())
{
h->push(other.h->top());
other.h->pop();
}
}
void elim(int slope)
{
while(a > slope)
{
b += h->top();
h->pop();
--a;
}
}
void shift(int len)
{
b -= len;
int poz1 = h->top();
h->pop();
int poz2 = h->top();
h->pop();
h->push(poz1 + len);
h->push(poz2 + len);
}
};
funct f[nmax + 5];
void dfs(int nod)
{
if(nod > n)
{
f[nod].a = 1;
f[nod].b = -c[nod];
f[nod].h->push(c[nod]);
f[nod].h->push(c[nod]);
return;
}
for(auto it : G[nod])
{
dfs(it);
f[nod] += f[it];
}
f[nod].elim(1);
f[nod].shift(c[nod]);
}
signed main()
{
ios::sync_with_stdio(false);
cin.tie(0);
cin>>n>>m;
for(int i=2;i<=n+m;i++)
{
cin>>t[i]>>c[i];
G[t[i]].push_back(i);
}
dfs(1);
f[1].elim(0);
cout<<f[1].b<<'\n';
return 0;
}
