#include <stdio.h>
#include <stdlib.h>
 
int main ()
{
    int n, i, j;
    long k = 0, *p;
    freopen ("fractii.in", "r", stdin);
    freopen ("fractii.out", "w", stdout);
    scanf ("%d", &n);
    p = malloc (n * sizeof (int));
    for (i = 1; i <= n; i++)
	    p[i] = i;
    for (i = 2; i <= n; i++)
    {
	    if (p[i] == i)
	    {
		    for (j = i; j <= n; j += i)
		    {
			    p[j] = p[j] / i * (i - 1);
		    }
	    }
	    k += (2 * p[i]);
    }
    k++;
    printf ("%ld", k);
    return 0;
}