#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int MAXN = 3e5+7;
vector< int >children[MAXN];
int parent[MAXN];
int weight[MAXN];
struct SlopeTrickable {
priority_queue< LL >slopeChanges;
LL m, c; ///mx + c is the rightmost line
void throwSlopesGreaterThan(LL g) {
while (m > g) {
///mx + c = (m-1)x + (x+c)
m -= 1;
c += slopeChanges.top();
slopeChanges.pop();
}
}
};
void merge(SlopeTrickable &from, SlopeTrickable &to) {
if (from.slopeChanges.size() > to.slopeChanges.size())
swap(from, to);
while (!from.slopeChanges.empty()) {
to.slopeChanges.push(from.slopeChanges.top());
from.slopeChanges.pop();
}
to.m += from.m;
to.c += from.c;
}
SlopeTrickable subtree[MAXN];
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
for (int i = 2; i <= n+m; i++) {
cin >> parent[i] >> weight[i];
children[parent[i]].push_back(i);
}
for (int i = n+1; i <= n+m; i++) {
subtree[i].slopeChanges.push(weight[i]);
subtree[i].slopeChanges.push(weight[i]);
subtree[i].m = 1;
subtree[i].c = -weight[i];
}
for (int i = n; i > 0; i--) {
for (int c : children[i]) {
merge(subtree[c], subtree[i]);
}
subtree[i].throwSlopesGreaterThan(1);
if (i > 1) {
LL x1 = subtree[i].slopeChanges.top();
subtree[i].slopeChanges.pop();
LL x0 = subtree[i].slopeChanges.top();
subtree[i].slopeChanges.pop();
subtree[i].slopeChanges.push(x0+weight[i]);
subtree[i].slopeChanges.push(x1+weight[i]);
subtree[i].c -= weight[i];
}
}
cout << subtree[1].slopeChanges.top() + subtree[1].c << "\n";
return 0;
}
