#include <bits/stdc++.h>
using namespace std;
#define int long long
using ll = long long;
#define fi first
#define se second
#define pb push_back
#define all(a) a.begin(),a.end()
#define sz(a) (int)a.size()
const int maxn = 5e3+10;
int p[maxn], c[maxn];
int n, m, ans;
vector<int> v;
vector<pair<int,int>> adj[maxn];
int32_t main() {
cin >> n >> m;
for(int i = 2; i <= n+m; i++){
cin >> p[i] >> c[i];
adj[i].pb({p[i],c[i]});
adj[p[i]].pb({i,c[i]});
}
for(int i = n+1; i <= n+m; i++) v.pb(c[i]);
sort(all(v)); int ans = 0;
for(auto u : v) ans+=abs(u-v[sz(v)/2]);
cout << ans;
}
