#include <bits/stdc++.h>
using namespace std;
struct Node {
long long m = 0, c = 0;
priority_queue<long long> pq;
void Merge(Node &o) {
m += o.m;
c += o.c;
if (pq.size() < o.pq.size()) {
swap(pq, o.pq);
}
while (!o.pq.empty()) {
pq.emplace(o.pq.top());
o.pq.pop();
}
}
void Process(long long C) {
while (m > 1) {
m--;
c += pq.top();
pq.pop();
}
long long u = pq.top(); pq.pop();
long long v = pq.top(); pq.pop();
c -= C;
pq.emplace(v + C);
pq.emplace(u + C);
}
long long Evaluate() {
return m * pq.top() + c;
}
};
int main() {
ios::sync_with_stdio(0);
cin.tie(0), cout.tie(0);
int N, M;
cin >> N >> M;
vector<int> P(N + M), C(N + M);
for (int i = 1; i < N + M; i++) {
cin >> P[i] >> C[i];
}
vector<Node> node(N + M);
for (int i = N + M - 1; i >= 0; i--) {
if (i >= N) {
node[i].m = 1;
node[i].c = -C[i];
node[i].pq.emplace(C[i]);
node[i].pq.emplace(C[i]);
} else {
node[i].Process(C[i]);
}
if (i > 0) {
node[--P[i]].Merge(node[i]);
}
}
cout << node[0].Evaluate() << "\n";
return 0;
}
