#include <iostream>

using namespace std;

ifstream fin;
ofstream fout;

long long sieve[1000001];
int n;

int main(int argc, char const *argv[])
{
	fin.open( "fractii.in" );
	fin >> n;
	fin.close();

	int result;
	for( int i = 1; i <= n; ++i ) sieve[i] = 0;
	sieve[1] = n;
	result = n;
	for( int i = 2; i <= n; ++i )
	{
		for( int j = i; j <= n; j += i )
		{
			sieve[i] += ( i - 1 );
		}
		result += sieve[i];
	}

	ofstream fout( "fractii.out" );
	fout << result;
	fout.close(); 
	return 0;
}