#include <fstream>

using namespace std;

bool viz[2000002];

int main() {
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	int n;
	f >> n;
	int nr = 1;
	if (n < 2) {
		g << 0;
	}
	else {
		if (n == 2) {
			g << 1;
		}
		else {
			for (int i = 3; i <= n; i = i + 2) {
				if (viz[i] == 0) {
					++nr;
					for (int j = 2 * i; j <= n; j += i) {
						viz[j] = 1;
					}
				}
			}
			g << nr;
		}
	}

	return 0;
}