#include <stdio.h>
#define N 1000000

int n,p[N];
long long sum=1;

int main()
{
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	
	scanf("%d",&n);
	
	for(int i=1;i<=n;i++)
		p[i]=i-1;
	for(int i=2;i*2<=n;i++)
		for(int j=2*i;j<=n;j+=i)
			p[j]-=p[i];
	
	for(int i=1;i<=N;i++)
		sum+=2*p[i];
	printf("%lld",sum);
	return 0;
}