#include <stdio.h>
#include <stdlib.h>
long long e[1000000];
int main()
{   FILE *fin,*fout;
  long long suma;
  int i,n,j;
    fin=fopen("fractii.in","r");
    fout=fopen("fractii.out","w");
    fscanf(fin,"%d",&n);
    for(i=1;i<=n;i++){
      e[i]=i;
    }
    for(i=2;i<=n;i++){
        if(e[i]==i){
            for(j=i;j<=n;j+=i){
                e[j]=e[j]/i*(i-1);
            }

        }

    }
    suma=1;
    for(i=2;i<=n;i++){
        suma+=2*e[i];
    }
    fprintf(fout,"%lld",suma);
    fclose(fin);
    fclose(fout);
    return 0;
}