#include <fstream.h>
int main()
{ long long i,j,fr,x,y,r;
long n;
ifstream f("fractii.in");
ofstream g("fractii.out");
f>>n;
int d,nrf,nrp;
nrf=1;
for (i=2;i<=n;i++)
  {x=i;
   nrp=i;
   d=2;
   while (x!=1)
   { if(x%d==0)
	     { while (x%d==0) x/=d;
	       nrp*=d-1;
	       nrp/=d;
	       }
      d++;
       }
   nrf+=(2*nrp);
   }
g<<nrf;
f.close();
g.close();
return 0;
}