#include<stdio.h>   

int main()   
{   
     int n,i,j,e[1000000];   
     long long s=1;
	 freopen("fractii.in","r",stdin);   
     freopen("fractii.out","w",stdout);   
     scanf("%d",&n);   
     for(j=1;j<=n;j++)   
         e[j]=j;   
     for(i=2;i<=n;i++)   
     {   
         if (e[i]==i)   
             for(j=i;j<=n;j+=i)   
                 e[j]=e[j]/i*(i-1);   
     }   
     for(i=2;i<=n;i++)   
        s=s+2*e[i];   
       
    printf("%lld\n",s);   
    return 0;   
}