#include <fstream>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");

#define maxn 1000005
int i,j,N;
int phi[maxn];
long long S;

int main()
{
	fin >> N;
	for(i=2;i<=N;i++) phi[i]=i;
	for(i=2;i<=N;i++)
		if(phi[i]==i)
			for(j=i;j<=N;j+=i)
				phi[j]=phi[j]/i*(i-1);
	S=1;
	for(i=2;i<=N;i++)
		S+=2*phi[i];
	fout << S;
}