#include <fstream>
using namespace std;

bool v[1999999];

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