#include<fstream.h>

double n;

double era(double n)
{  
   int i, j, nr = 1,p[500];  
   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;
}