/*input
4 6
1 5
2 5
2 8
3 3
3 2
3 3
2 9
4 4
4 3
*/
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;
struct Curve : priority_queue<int>
{
int end_slope;
long long offset;
void swap(Curve &rhs)
{
priority_queue::swap(rhs);
std::swap(end_slope, rhs.end_slope);
std::swap(offset, rhs.offset);
}
void init(int x)
{
while (!empty()) pop();
push(x), push(x);
end_slope = 1;
offset = 0;
}
void merge(Curve &rhs)
{
if (size() < rhs.size()) swap(rhs);
if (rhs.empty()) return;
if (top() < rhs.top()) offset = offset + rhs.offset + (long long) end_slope * (rhs.top() - top());
else offset = offset + rhs.offset + (long long) rhs.end_slope * (top() - rhs.top());
end_slope += rhs.end_slope;
for (; !rhs.empty(); rhs.pop()) push(rhs.top());
}
void normalize(int x)
{
for (; end_slope > 1; --end_slope) {
int t = top();
pop();
offset -= (long long) (t - top()) * (end_slope - 1);
}
int first = top();
pop();
int second = top();
pop();
push(second + x);
push(first + x);
}
};
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0);
int N, M;
cin >> N >> M;
vector<int> P(N + M + 1), C(N + M + 1);
for (int i = 2; i <= N + M; ++i) cin >> P[i] >> C[i];
vector<Curve> curves(N + M + 1);
for (int i = N + M; i > N; --i) {
curves[i].init(C[i]);
curves[P[i]].merge(curves[i]);
}
for (int i = N; i > 1; --i) {
curves[i].normalize(C[i]);
curves[P[i]].merge(curves[i]);
}
curves[1].normalize(0);
cout << curves[1].offset << endl;
}
