#include <fstream>
bool p[2000001];
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
int main() {
	int n;
	cin >> n;
	int contor = 0;
	for (int i = 2; i * i <= n; i++) {
		if (!p[i]) {
			for (int j = i * i; j <= n; j+=i)
				p[j] = 1;
		}
	}
	for (int i = 2; i <= n; i++)
		if (!p[i])
			++contor;
	cout << contor;

}