#include<fstream>
#define NMAX 1000002
using namespace std;
long a[NMAX],i,j,n;
long long s;
int main()
{
ifstream f("fractii.in");
f>>n;
f.close();
s=1;
a[1]=1;
for (i=2;i<=n;i++)
	a[i]=i;
for (i=2;i<=n;i++)
{
	if (a[i]==i)
	{
		s+=2*(i-1);
		a[i]--;
		for (j=i+i;j<=n;j+=i)
		{
			a[j]=(a[j]/i)*(i-1);
		}		
	}
	else
	{
		s+=2*a[i];
	}
}
ofstream g("fractii.out");
g<<s<<'\n';
g.close();

return 0;
}