#include <fstream>

using namespace std;

const int MAX = 3e6 ;

bool v [ MAX ] ;

int solve ( int n )
{
    int sol = 0 ;
    for ( int i = 2 ; i <= n ; ++ i )
    {
        if ( v [ i ] == 0 ) /// e prim
        {
            ++ sol ;
            for ( int j = i + i ; j <= n ; j += i )
                v [ j ] = 1 ;
        }
    }
    return sol ;
}

int main()
{
    int n ;
    cin >> n ;
    cout << solve ( n ) ;
    return 0;
}