#include<iostream>
#include<fstream>
		 using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int n,i;
double sol=1;
double calc_phi(int l)
{
int k=l;
double phi=k;
i=2;
while(k!=1)
{if (k%i==0) {
    while(k%i==0) k/=i;
    phi*=(double)(i-1)/i;
    }
     i++;
	   }
    return phi;
    }


int main()
{
    f>>n;
for(int l=2;l<=n;l++)
	sol+=calc_phi(l)*2;
            
            g<<sol;
	    f.close();
            g.close();
            return 0;
    }