#include<stdio.h>
main()
{
long long n,j,i,tot,a[1000000];
FILE *f,*g;
f=fopen("fractii.in","r");
g=fopen("fractii.out","w");
fscanf(f,"%lld",&n);
tot=1;
for(i=2;i<=n;i++)
 a[i]=i;
for(i=2;i<=n/2;i++)
 if(a[i]==i)
   for(j=2;j<=(n/i);j++)
     a[i*j]=(a[i*j]*(i-1))/i;
for(i=1;i<=n;i++)
 if(a[i]==i)tot=tot+(i-1)*2;
 else tot = tot+a[i]*2;
fprintf(g,"%lld \n",tot);

fclose(f);
fclose(g);
return 0;
}