#include <iostream>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream o("ciur.out");

int is_prime[2000005] = { 0 }, nr_of_primes = 0, n;

int main()
{
    

    f >> n;

    for (int i = 2; i <= n; i++) {


        if (is_prime[i] == 0) {


            for (int j = i * i; j <= n; j += i) {


                is_prime[j] = 1;


            }


           


            nr_of_primes++;


        }


    }
    cout << nr_of_primes;
    return 0;
}