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

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