#include <bits/stdc++.h>
using namespace std;
int main(){
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];
P[i]--;
}
vector<vector<int>> c(N + M);
for (int i = 1; i < N + M; i++){
c[P[i]].push_back(i);
}
vector<long long> mn(N + M, 0);
vector<priority_queue<long long>> L(N + M);
vector<priority_queue<long long, vector<long long>, greater<long long>>> R(N + M);
for (int i = N; i < N + M; i++){
L[i].push(0);
R[i].push(0);
}
for (int i = N - 1; i >= 0; i--){
for (int j : c[i]){
long long x = L[j].top();
L[j].pop();
L[j].push(x + C[j]);
long long y = R[j].top();
while (!R[j].empty()){
R[j].pop();
}
R[j].push(y + C[j]);
}
for (int &j : c[i]){
if (L[j].size() > L[c[i][0]].size()){
swap(j, c[i][0]);
}
}
swap(mn[i], mn[c[i][0]]);
swap(L[i], L[c[i][0]]);
swap(R[i], R[c[i][0]]);
for (int j : c[i]){
if (j != c[i][0]){
mn[i] += mn[j];
while (!R[j].empty()){
long long a = R[j].top();
R[j].pop();
if (!L[i].empty()){
mn[i] += max(L[i].top() - a, (long long) 0);
}
L[i].push(a);
R[i].push(L[i].top());
L[i].pop();
}
while (!L[j].empty()){
long long a = L[j].top();
L[j].pop();
if (!R[i].empty()){
mn[i] += max(a - R[i].top(), (long long) 0);
}
R[i].push(a);
L[i].push(R[i].top());
R[i].pop();
}
}
}
}
cout << mn[0] << endl;
}
