#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

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

int n,i,j;
int np[1000005];
long long rez=1;

int main () {
	
	fin>>n;
	for(i=1;i<=n;i++)
		np[i]=i;
	for(i=2;i<=n;i++)
	{
		if(np[i]==i)
			for(j=i;j<=n;j+=i)
				np[j]=np[j]/i*(i-1);
		rez+=(2LL*np[i]);
	}
	fout<<rez<<"\n";
}