#include<stdio.h>
#define N 1000001
long a[N],v[N],n;
void ER()
	{
	long i,j;
	for(i=2;i<=n;i++)
	v[i]=i;
	for(i=2;i<=n;i++)
	{
	if(!a[i])
		{
		j=1;
		while(i*j<=n)
			{
			a[i*j]=1;
			v[i*j]=v[i*j]-(v[i*j]/i);
			j++;
			}
		}
	}
}
int main()
	{
	long long i,j,solutie=1;
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	scanf("%lld",&n);
	ER();
	for(i=2;i<=n;i++)
	solutie+=2*v[i];
	printf("%lld",solutie);
	return 0;
	}