#include <fstream>
using namespace std;

ifstream in("fractii.in");
ofstream out("fractii.out");

int v[1000001],n;
long long s=1;

void euler()
{
	int i,j;
	for (i=1; i<=n;i++)
		v[i]=i;
	for (i=2;i<=n;i++)
		if(v[i]==i)
			for(j=i;j<=n;j+=i)
				v[j]=v[j]/i*(i-1);
}
	
int main()
{
	int i;
	in>>n;
	euler();
	for (i=2;i<=n;i++)
		s+=2*v[i];
	out<<s;
	return 0;
}