#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 300500;
int n, m;
int p[N];
ll c[N];
vector<int> g[N];
ll base[N];
ll d[N];
priority_queue<ll, vector<ll>> q[N];
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
cin >> n >> m;
for (int i = 1; i < n + m; ++i) {
cin >> p[i] >> c[i];
--p[i];
g[p[i]].push_back(i);
}
c[0] = 0;
for (int i = n; i < n + m; ++i) {
base[i] = c[i];
d[i] = -1;
q[i].push(c[i]);
q[i].push(c[i]);
}
for (int i = n - 1; i >= 0; --i) {
int mx = g[i][0];
for (int j : g[i]) {
if (q[i].size() > q[mx].size()) {
mx = j;
}
base[i] += base[j];
d[i] += d[j];
}
swap(q[i], q[mx]);
for (int j : g[i]) {
if (j != mx) {
while (!q[j].empty()) {
q[i].push(q[j].top());
q[j].pop();
}
}
}
while (d[i] + q[i].size() > 1) {
q[i].pop();
}
ll x = q[i].top();
q[i].pop();
ll y = q[i].top();
q[i].pop();
q[i].push(x + c[i]);
q[i].push(y + c[i]);
base[i] += c[i];
}
vector<ll> a;
while (!q[0].empty()) {
a.push_back(q[0].top());
q[0].pop();
}
reverse(a.begin(), a.end());
ll ans = base[0];
ll diff = d[0];
if (diff < 0) {
ans += diff * a[0];
}
for (int i = 0; i < (int)a.size() - 1; ++i) {
diff += 1;
ans += diff * (a[i + 1] - a[i]);
}
cout << ans << endl;
return 0;
}
