#include <bits/stdc++.h>
#define ll long long
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define pb push_back
#define FIO ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)
using namespace std;
ll nxt() {ll num; cin >> num; return num;}
const int N = 307;
int n, m;
vector <pair <ll, ll> > adj[N];
ll dis[N];
void dfs(int x) {
for (auto it : adj[x]) {
dis[it.F] = dis[x] + it.S;
}
}
int main () {
cin >> n >> m;
for (int i = 2; i <= n+m; i++) {
ll p, c; cin >> p >> c;
adj[p].pb({i, c});
}
dfs(1);
if (n == 1) {
vector <int> v;
for (int i = 1; i <= m; i++) {
v.pb(dis[i+n]);
}
sort(all(v));
ll sr = v[(m-1)/2], cost = 0;
for (int i = 1; i <= m; i++) {
cost += abs(dis[i+n] - sr);
}
cout << cost;
return 0;
}
return 0;
}
