#include <stdio.h>
#include <stdlib.h>

int v[1000006];

int main(){
  long long n,i,j,s;
  FILE *fin,*fout;
  fin=fopen("fractii.in","r");
  fout=fopen("fractii.out","w");
  fscanf(fin,"%lld",&n);

  for(i=2;i<=n;i++){
    v[i]=i;
  }

  for(i=2;i<=n;i++){
    if(v[i]==i){
      for(j=i;j<=n;j+=i){
        v[j]=v[j]/i*(i-1);
      }
    }
  }

  s=1;
  for(i=2;i<=n;i++){
    s+=v[i]*2;
  }

  fprintf(fout,"%lld",s);

  fclose(fin);
  fclose(fout);
  return 0;
}