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

int main() {
    ll n,sol=0,x,y;
    cin >> n;
    for (int i=1;i<=n;i++) {
        x=n/i;
        y=(x+1)*x/2;
        sol+=i*y;
    }
    cout << sol;
}
