#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;
ifstream fin("ciur.in") ;
ofstream fout("ciur.out") ;


int main ()
{
    int a[100] , i , n , cont = 0 , j ;
    fin >> n ;
    for ( i = 1 ; i <= n ; i++ )
        a[i] = 0 ;
    a[0] = 1 ;
    a[1] = 1 ;
    for ( i = 2 ; i <= sqrt(n) ; i++ )
        {
            if ( a[i] == 0 )
                {
                    for ( j = 2 ; j <= n/i ; j++ )
                            a[ i*j ] = 1 ;
                }
        }
    for ( i = 2 ; i <= n ; i++ )
        {
            if ( a[i] == 0 )
                cont++ ;
        }
    fout << cont ;
    return 0 ;
}