#include<stdio.h>
FILE *f=fopen("fractii.in","r"),
     *g=fopen("fractii.out","w");
int a[1000007],i,j,n,k;
long long s;
int main()
{ fscanf(f,"%d",&n);
  for(i=2;i<=n;++i) { if(a[i]==0)   for(j=i;j<=n;j+=i){ if(a[j]==0) a[j]=j;
							a[j]/=i;
							a[j]*=i-1;
						      }
		      s+=a[i]*2;
		    }
  fprintf(g,"%lld\n",s+1);
  fclose(f);
  fclose(g);
  return 0;
}