#include<cstdio>

const int N=1000001;

void euler(int n,int e[N])
{
	int i,j;
	for(i=2;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);
}

long long calcul(int n)
{
	int e[N];
	long long s=0;
	euler(n,e);
	for(int i=2;i<=n;++i)
		s+=e[i];
	return 1+(s<<1);
}

int main()
{
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	int n;
	scanf("%d",&n);
	printf("%lld\n",calcul(n));
	return 0;
}