#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vll = vector <ll>;
using ii = pair <ll, ll>;
using vii = vector <ii>;
const ll MAXN = 3E2+16, INF = ll(1E18)+16;
vii adj[MAXN];
ll dp[MAXN][MAXN];
void dfs (ll u) {
if (adj[u].empty()) iota(dp[u], dp[u]+MAXN, 0);
for (auto [v, w] : adj[u]) {
dfs(v);
for (ll i = 0; i <= 300; i++) { // wanted expl time
ll minN = INF;
for (ll mod = 0; mod <= i; mod++) { // mod on w
minN = min(minN, dp[v][i-mod]+abs(mod-w));
}
dp[u][i] += minN;
}
}
}
int main () {
cin.tie(nullptr) -> sync_with_stdio(false);
ll n, m;
cin >> n >> m;
for (ll v = 1; v < n+m; v++) {
ll u, w;
cin >> u >> w;
u--;
adj[u].push_back({ v, w });
}
dfs(0);
ll ans = INF;
for (ll i = 0; i <= 300; i++) {
ans = min(ans, dp[0][i]);
}
cout << ans << '\n';
return 0;
}
