#include <fstream>
using namespace std;

bool v[1999999];

int main() {
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	int n;
	fin >> n;
	int cnt_prime_numbers = 1;
	for (int i = 3; i * i <= n; i += 2) {
		for (int k = 3; i * k <= n; k += 2) {
			v[i * k] = true;
		}
	}
	for (int i = 3; i <= n; i += 2) {
		if (!v[i]) {
			++cnt_prime_numbers;
		}
	}
	fout << cnt_prime_numbers;
	return 0;
}