#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 3e2 + 10, INF = 1e9;
ll n, m, dp[MAXN][MAXN], sum[MAXN];
vector<pair<ll, ll>> adj[MAXN];
void input() {
cin >> n >> m;
for (int i = 1; i < n + m; i++) {
ll u, w;
cin >> u >> w;
adj[--u].push_back({i, w});
}
for (int i = 0; i < n + m; i++)
for (int j = 0; j < MAXN; j++)
dp[i][j] = INF;
}
void dfs(int u) {
if ((int)adj[u].size() == 0) {
dp[u][0] = 0;
return;
}
for (auto v : adj[u])
dfs(v.first);
for (int i = 0; i < MAXN; i++)
sum[i] = 0;
for (auto v : adj[u])
for (int i = 0; i < MAXN; i++) {
ll mi = INF;
for (int j = 0; j <= i; j++)
mi = min(mi, dp[v.first][j] + abs(v.second - (i - j)));
sum[i] += mi;
}
for (int i = 0; i < MAXN; i++)
dp[u][i] = min(dp[u][i], sum[i]);
}
ll findAns() {
ll res = INF;
for (int i = 0; i < MAXN; i++)
res = min(res, dp[0][i]);
return res;
}
int main() {
ios::sync_with_stdio(false); cin.tie(0);
input();
dfs(0);
cout << findAns() << endl;
return 0;
}
