#include <fstream>
using namespace std;

int v[2000001];

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