#include <stdio.h>
#define max 1000005
int n,e[max];
void euler()
{
	int j,i;
	for (i=2; i<max; i++)
		e[i]=i;
	for (i=2; i<max; i++)
		if (e[i]==i)
			for (j=i; j<max; j+=i)
				e[j]=e[j]/i*(i-1);
}
long long rez()
{
	int i;
	long long suma=1;
	for (i=2; i<=n; i++)
		suma=suma+2*e[i];
	return suma;
}
int main()
{
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	scanf("%d",&n);
	euler();
	printf("%lld",rez());
	return 0;
}