#include <iostream>
#include <fstream>

using namespace std;

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

int n ;
char a[2000001] ;

void Citire()
{
    fin >> n;
}
int nr = 0 ;

void CiurEratostene (int n)
{
    int i , j ;
    for ( i = 2 ; i <= n ; ++ i )
            a[i] = 1;

    for( i = 2 ; i <= n ; ++ i )
        if ( a[i] == 1 )
            {
                   ++ nr ;
                   for ( j = i+i ; j <= n ; j += i )
                               a[j] = 0;
            }
     fout << nr ;

}
int main()
{
    Citire();
    CiurEratostene(n);
    return 0;
}