#include <iostream>
#include <fstream>
using namespace std;

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

int n, rez, prime[2000005];

int main() {
	in >> n;

	for (int i = 2; i < n; i++) {
		prime[i] = 1;
	}

	for (int i = 2; i < n; i++) {
		if (prime[i]) {
			rez++;
			for (int j = 2 * i; j < n; j += i) {
				prime[j] = 0;
			}
		}
	}

	out << rez;
}