#include<fstream.h>

double n;
#define lol = 1000001;  


double era(double n)
{   double p[lol];    
   int i, j, nr = 1;  
   for (i=1;((i*i)<<1)+(i<<1)<=n;i+=1) 
   {        
     if((p[i>>3]&(1<<(i&7)))==0)
      {  
       for(j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
        {  
         p[j>>3]|=(1<<(j&7));  
       }  
     }  
   }  
   for (i=1;2*i+1<=n;++i)    
        if ((p[i>>3]&(1<<(i&7)))==0)   
            nr++;  
   return nr;  
}

int main()
{   ifstream f("fractii.in");
   f>>n;   
   f.close();
  ofstream g("fractii.out");
  double omfg,i;
  
  omfg=0;
  
  for(i=era(n);i;i--)
   omfg=omfg+i;
   
  g<<n+omfg;
  
       
    return 0;
}