using namespace std;
int c[100000]={0},n,p=1;
void ciur()
{
	for(i=2;i<=n;++i)
	   if(!c[i])
	       for(int j=i*i;j<=n;j++)
		       c[j]=1;
}	
int euler(int a)
{
	int s=sqrt(a),re=a;
	for(int i=2;i<=s;++i)
	    if(!c[i])
		    if(a%i==0)
			    re=re/i*(i-1);
 return re*2;
}
			    
}
int main()
{
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	scanf("%d",&n);
	ciur();
	for(int i=2;i<=n;++i)
	    p+=euler(i);
	printf("%d",&p);
	return 0;
}