#include<fstream>
using namespace std;
long long phi[1000100],n,s=1;
int main() {
	int i,j;
	ifstream in("fractii.in");
	in>>n;
	in.close();
	for(i=1;i<=n;phi[i]=i,i++);
	for(i=2;i<=n;i++)
		if(phi[i]==i)
			for(j=i;j<=n+1;j+=i)
				phi[j]=phi[j]/i*(i-1);
	ofstream out("fractii.out");
	for(i=2;i<=n;s+=2*phi[i],i++);
	out<<s<<'\n';
	out.close();
	return 0;
}