#include <iostream>

#include <fstream>



using namespace std;



ifstream in ("ciur.in");

ofstream out ("ciur.out");



bool ciur [2000001];

int main() {

    int n;

    in >> n;

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

        if (!ciur [i]) {

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

                ciur [j] = true;

            }

        }

    }

    int prime = 0;

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

        if (!ciur [i])

            prime ++;

    }

    out << prime;

    return 0;

}