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