#include<bits/stdc++.h>
using namespace std;
#define int long long
#define nl '\n'
const int N = 300001;
vector<pair<int,int>> g[N];
inline void solve(){
int n, m;
cin>>n>>m;
vector<int> v;
for(int i=2; i<=n+m; i++){
int p, c;
cin>>p>>c;
g[p].push_back({i, c});
v.push_back(c);
}
sort(v.begin(), v.end());
int x = v[m/2];
int ans = 0;
for(int y : v) ans += abs(x-y);
cout<<ans;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);cout.tie(NULL);
int t = 1;
//cin>>t;
while(t--) solve();
return 0;
}
