#include<stdio.h>
int main()
{
	int n,i,j,e[1000001];
	long long s=1;
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		e[i]=i;
	for(i=2;i<=n;i++)
	{
		if(e[i]==i)
		{
			for(j=i;j<=n;j+=i)
				e[j]=e[j]/i*(i-1);
		}
	}
	for(i=2;i<=n;i++)
		s=s+2*e[i];
	printf("%lld",s);
	return 0;
}