#include <fstream>
using namespace std;
ifstream cin("eratostene.in");
ofstream cout("eratostene.out");

bool v[2000000], n;

int main() {
	cin >> n;
	v[0] = 1;
	v[1] = 1;
	for (int i = 2; i * i <= n; ++i) {
		if (v[i] == 0)
		for (int k = 2; k <= n / i; ++k) {
			v[i * k] = 1;
		}
	}
	int c = 0;
	for (int i = 2; i <= n; ++i)
		if (v[i] == 0)
			c++;
	cout << c;

	return 0;
}