#include<fstream> 
#define N 1000010

using namespace std; 

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

int n,phi[N]; 

void calcul () 
{ 
	for(int i=1;i<=n;i++) 
		phi[i]=i;
	for(int i=2;i<=n;i++) 
	{ 
		if(phi[i]==i) 
		{ 
			for(int j=i;j<=n;j=j+i) 
				phi[j]=(phi[j]/i)*(i-1);
		}
	} 
} 

int main ()
{ 
	long long s=-1;
	in>>n; 
	calcul ();
	for(int i=1;i<=n;i++) 
		s=s+2*phi[i];
	out<<s; 
	in.close (); 
	out.close (); 
	return 0;
}