#include <bits/stdc++.h>
using ll = long long;
using namespace std;

int main() {
    int n;cin>>n;
    ll ans=0;
    for (int i=1;i<=n;i++) {
        ll d=n/i;
        ans+=d*(d+1)/2*i;
    }
    cout<<ans<<endl;
    return 0;
}