#include <stdio.h>
int a[1000000];
long functi(int n,int a[1000000])
{
	int i,j;
	long long k=0;
	for (i=2;i<=n;i++)
		a[i]=i;
	for (i=2;i<=n;i++)
	{
		for (j=2*i;j<=n;j=j+i){
			a[j]=a[j]=a[i];
		}
		k=k+a[i];
		}
	k=2*k;

return k-1;
}
int main()
{
	int n;
	
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	scanf("%d",&n);
	printf("%lli",functi(n,a));
	return 0;
}