#include<stdio.h>  
    
  #define N 1000001  
    
  int n,v[N];  
    
  void euler()  
  {  
      int i,j;  
      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 ) ;  
  }  
    
  void calcul()  
  {  
      long long s=1;  
      int i;    
      for( i=2 ; i<=n ; ++i )  
          s+= 2 * v[i];  
      printf("%lld",s);  
        
  }  
    
  int main()  
  {  
      freopen("fractii.in","r",stdin);  
      freopen("fractii.out","w",stdout);  
      scanf("%d",&n);  
      euler();  
      calcul();  
        
      return 0;  
  }