#include <iostream>
#include <stdio.h>

using namespace std;

bool v[2000001] ;

int main()
{
    int n ;
    freopen( "ciur.in" , "r" , stdin ) ;
    freopen( "ciur.out" , "w" , stdout ) ;
    scanf( "%i" , &n ) ;
    for ( int i = 2 ; i <= n ; i ++ )
        if ( v[i] == 0 )
           for ( int j = i + i ; j <= n ; j += i )
              v[j] = 1 ;
    int sum = 0 ;
    for ( int i = 2 ; i <= n ; i ++ )
        if ( v[i] == 0 )
           sum ++ ;
    cout << sum << "\n" ;
    return 0;
}