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

int	main()
{
	int	N;
	cin >> N;
	int64_t	sum = 0;
	for (int i = 1; i < N + 1; ++i) {
		for (int j = i; j < N + 1; j += i) {
			sum += j;
		}
	}
	cout << sum << endl;
}
