#include <bits/stdc++.h>
using namespace std;
#define int long long
const int MAXN = 5e3 + 25;
vector <pair <int, int>> adj[MAXN];
int dp[MAXN][301], n, m;
void dfs (int pos) {
for (auto j : adj[pos]) {
dfs(j.first);
}
if(adj[pos].empty()) {
for (int i = 1; i <= 300; i++) dp[pos][i] = 1e18;
return;
}
for (int i = 0; i <= 300; i++) {
int sum = 0;
for (auto j : adj[pos]) {
int mn = 1e18;
for(int k = 0; k <= i; k++) mn = min(mn, abs(j.second - i + k) +dp[j.first][k]);
sum += mn;
}
dp[pos][i] = sum;
}
}
signed main () {
cin >> n >> m;
n += m;
for (int i = 2; i <= n; i++) {
int x, y; cin >> x >> y;
adj[x].push_back({i, y});
}
dfs(1);
int mn = 1e18;
for (int i = 0; i <= 300; i++) mn = min(mn, dp[1][i]);
for (int i = 1; i <= n - m; i++) {
for (int j = 1; j < 300; j++) {
assert(dp[i][j] - dp[i][j - 1] <= dp[i][j + 1] - dp[i][j]);
}
}
cout << mn << '\n';
}
