#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=3e5+10;
int n, m;
priority_queue<int> pq[N];
int a[N], b[N], p[N], c[N];
void merge(int u, int v){
if (pq[u].size()<pq[v].size()) pq[u].swap(pq[v]), swap(a[u], a[v]), swap(b[u], b[v]);
while (pq[v].size()) pq[u].push(pq[v].top()), pq[v].pop();
a[u]+=a[v];
b[u]+=b[v];
}
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
for (int i=2; i<=m+n; ++i){
cin >> p[i] >> c[i];
}
for (int i=n+m; i>n; --i){
pq[i].push(c[i]);
pq[i].push(c[i]);
a[i]=1; b[i]=-c[i];
merge(p[i], i);
}
for (int i=n; i>=2; --i){
while (a[i]>1){
b[i]+=pq[i].top();
pq[i].pop();
--a[i];
}
int t1=pq[i].top(); pq[i].pop();
int t2=pq[i].top(); pq[i].pop();
pq[i].push(t2+c[i]);
pq[i].push(t1+c[i]);
b[i]-=c[i];
merge(p[i], i);
}
while (a[1]>0){
b[1]+=pq[1].top();
pq[1].pop();
--a[1];
}
cout << b[1] << '\n';
return 0;
}
