#include <fstream.h>
 
bool a[2000000];
   
 int main()  
{
	int i, j, n, nr = 0;
     ifstream fin("ciur.in");  
    fin >> n;  
    fin.close();  
ofstream fout("ciur.out");
    for ( i = 0; i < n; i++)
	 a[i] = true;
     for ( i = 2; i * i <= n; i++)
	 if ( a[i] )
	 {
	     j = 2;
	     while ( i*j < n )
	     {
		 a[i*j] = fals;
                 j++;  
             }  
         }  
     for ( i = 2; i <= n; i++)  
         if ( a[i] )  
         nr++;  
      fout << nr;  
      fout.close();  
       return 0;  
 }