#include<fstream>
using namespace std;
long long a[1000002],viz[1000001];
int main ()
{
	ifstream f("fractii.in");
	ofstream g("fractii.out");
	long long s=1,n,i,k;
	f>>n;
	for(i=2;i<=1000000;i++) a[i]=i;
	for(i=2;i<=1000000;i++)
		if(!viz[i])
		{
			a[i]--;
			k=2;
			while(k*i<=n)
			{
				viz[k*i]=1;
				a[k*i]=a[k*i]-a[k*i]/i;
				k++;
			}
		}
	for(i=2;i<=n;i++) s+=2*a[i];
	g<<s;
	f.close();g.close();
	return 0;
}