#include <fstream>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int n, cnt;
bool ciur[2000001];
void eratostene();

int main() {
	cin >> n;
	cnt = 1;
	eratostene();
	cout << cnt;
	return 0;
}

void eratostene() {
	for (int i = 3; i <= n; i += 2) {
		if (!ciur[i]) {
			cnt++;
			for (int j = 2; i * j <= n; j++) ciur[i * j] = 1;
		}
	}
}