#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn = 300 + 10;
const ll inf = 1e18;
vector<pair<int,int>> t[maxn];
ll dp[maxn][maxn];
int lo[maxn], r[maxn];
void dfs(int v){
if (t[v].empty()){
dp[v][0] = 0;
for (int j = 1; j < maxn; j++)
dp[v][j] = inf;
return;
}
for (auto [u,c] : t[v]){
dfs(u);
for (int i = 0; i < maxn; i++){
ll now = inf;
for (int j = 0; j <= i; j++)
now = min(now, dp[u][j] + abs(i-j-c));
dp[v][i] += now;
}
}
}
int main(){
ios_base::sync_with_stdio(false);
int n, m;
cin >> n >> m;
for (int i = 2; i <= n+m; i++){
int v, c;
cin >> v >> c;
t[v].push_back({i,c});
}
dfs(1);
ll answer = inf;
for (int i = 0; i < maxn; i++)
answer = min(answer, dp[1][i]);
cout << answer << endl;
}
