#include <fstream>
#include <math.h>

using namespace std;

int main()
{
    
    //toate numerele prime mai mici decat n\
    
    
    
    
    int n,k,i,prim,contor=0,radical;
    ifstream fin("ciur.in");
    fin>>n;
    fin.close();
    
    
    for(k=2;k<=n;k++)
       {
                     radical=(int)sqrt(k);
                     prim=1;
                     for(i=2;i<=radical;i++)
                        if (k%i==0) 
                        { prim=0;break;}
                        
                     if (prim==1)  contor++;
                     }
    ofstream fout("ciur.out");
    fout<<contor;
    fout.close();                 
                     
                     
      
       return 0;
       }