#include <fstream>

using namespace std;

int main()
{
	unsigned long n,i,j,sum,s;
	bool x[1000000];
	ifstream f("fractii.in");
	ofstream g("fractii.out");
	f>>n;
	f.close ();
	i = 2;
	sum = n;
	
	while (i<=n)
	{
		if (!x[i])
		{
			x[i] = true;
			j = i; s = 1;
			while ( (j+i)<=n )
			{
				s++;
				j+=i;
				x[j] = true;
			}
			sum = sum + (n - s)*s;
		}
		i++;
	}
	
	g<<sum;
	
	g.close();
	
	return 0;
}