#include <bits/stdc++.h>
using namespace std;
const int DIM = 300005;
struct Dp {
long long a, b;
priority_queue<long long> *points;
};
Dp dp[DIM];
int parent[DIM], length[DIM];
Dp merge(Dp str1, Dp str2) {
Dp ans;
ans.a = str1.a + str2.a;
ans.b = str1.b + str2.b;
if (str1.points -> size() > str2.points -> size()) {
ans.points = str1.points;
while (str2.points -> size()) {
ans.points -> push(str2.points -> top());
str2.points -> pop();
}
} else {
ans.points = str2.points;
while (str1.points -> size()) {
ans.points -> push(str1.points -> top());
str1.points -> pop();
}
}
return ans;
}
int main(void) {
// freopen("fireworks.in", "r", stdin);
// freopen("fireworks.out", "w", stdout);
int n, m;
cin >> n >> m;
for (int i = 1; i <= n + m; ++i) {
if (i > 1)
cin >> parent[i] >> length[i];
dp[i].points = new priority_queue<long long>();
}
for (int i = n + m; i > 1; --i) {
if (i > n) {
dp[i].a = 1; dp[i].b = -length[i];
dp[i].points -> push(length[i]);
dp[i].points -> push(length[i]);
} else {
while (dp[i].a > 1) {
long long x = dp[i].points -> top();
dp[i].a--; dp[i].b += x;
dp[i].points -> pop();
}
long long x = dp[i].points -> top();
dp[i].points -> pop();
long long y = dp[i].points -> top();
dp[i].points -> pop();
dp[i].points -> push(x + length[i]);
dp[i].points -> push(y + length[i]);
dp[i].b -= length[i];
}
dp[parent[i]] = merge(dp[parent[i]], dp[i]);
}
while (dp[1].a > 0) {
long long x = dp[1].points -> top();
dp[1].a--; dp[1].b += x;
dp[1].points -> pop();
}
cout << dp[1].b << endl;
return 0;
}
