#include <iostream>
#include <vector>
#include <cmath>
using namespace std;
int n, m;
vector< pair<int, int> > adj[310];
long long dp[310][310];
void dfs (int x) {
if (adj[x].size() == 0) {
dp[x][0] = 0;
for (int i=1; i<=300; i++) {
dp[x][i] = 1e16;
}
return;
}
for (auto i: adj[x]) {
dfs(i.first);
}
for (int i=0; i<=300; i++) {
for (auto j: adj[x]) {
long long best = 1e16;
for (int k=0; k<=i; k++) {
best = min(best, dp[j.first][k]+abs(i-k-j.second));
}
dp[x][i] += best;
}
}
}
int main () {
cin >> n >> m;
int pi, wi;
for (int i=2; i<=n+m; i++) {
cin >> pi >> wi;
adj[pi].push_back({i, wi});
}
dfs(1);
long long o = 1e16;
for (int i=0; i<=300; i++) {
o = min(o, dp[1][i]);
}
cout << o << endl;
}
