#include <fstream>

using namespace std;

int main() {
	int N, c = 0;
	ifstream f("ciur.in");
	f >> N;
	f.close();
	bool* A = new bool[N + 1];
	for (int i = 2; i <= N; ++i) {
		A[i] = true;
	}
	for (int i = 2; i <= N; ++i) {
		if (A[i]) {
			c++;
			for (int j = i + i; j <= N; j += i) {
				A[j] = false;
			}
		}
	}
	ofstream g("ciur.out");
	g << c << "\n";
	g.close();

	return 0;
}