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

int v[1000001];
long long rez;
int n;
void IndEuler(){
  int i,j;
  long long nr;
  for(i=1;i<=n;i++){
      v[i]=i;
  }
  for(i=2;i<=n;i++){
    if(v[i]==i){
      for(j=i;j<=n;j=j+i){
        v[j]=v[j]/i*(i-1);
      }
    }
  }
  for(i=2;i<=n;i++){
    rez=rez+v[i]*2;
  }
}
int main(){
    FILE *fin,*fout;
    fin=fopen("fractii.in","r");
    fout=fopen("fractii.out","w");
    fscanf(fin,"%d",&n);
    rez=1;
    IndEuler();
    fprintf(fout,"%lld",rez);
    fclose(fin);
    fclose(fout);
    return 0;
}