#include<fstream>
using namespace std;
#define MIL 1000003

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

bool Prime[MIL];
long long Sol,Phi[MIL];
int N;

void ciur(){
	int i,j;

	for(i=1;i<MIL;i++){
		if(!(i%2))
			Phi[i]=i/2;
		else
			Phi[i]=i;
	}
	
	for(i=3;i<=1000;i+=2){
		if(Phi[i]==i){
			for(j=i ; j<=N; j+=i){
				Phi[j]=Phi[j]/i*(i-1);
			}
		}
	}
	
	for(i=2;i<=N;i++){
		Sol+=2*Phi[i];
	}
}

int main(){
	
	fin>>N;
	Sol=1;
	
	ciur();
	
	fout<<Sol<<"\n";
	
	fin.close();
	fout.close();
	return 0;
}