#include<fstream.h>

long a[1000000];
long n,i,j,m,aux;
long long sum,c,p;

int main()
{
	ifstream f("factii.in");
	ofstream g("fractii.out");
	f>>n;
	sum=1;
	for (i=2;i<=n;++i) a[i]=i;
	for (i=2;i<=n;++i)
	if (a[i]==i) 
		for (j=i;j<=n;j+=i) a[j]=a[j]/i*(i-1);
	for (i=1;i<=n;i++)
		sum+=a[i]*2;
	g<<sum<<"\n";
	f.close();
	g.close();
}