#include <fstream>

using namespace std;

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

const int MAXN = 2e6;
int n, cnt;

bool c[MAXN + 1];
void ciur() {
	c[0] = 1;
	c[1] = 1;
	for (int i = 4; i <= n; i += 2) c[i] = 1;
	for (int i = 3; i <= n; i += 2) {
		if (!c[i]) {
			++ cnt;
			for (int j = i + i; j <= n; j += i)
				c[i] = 1;
		}
	}
}

int main() {
	in >> n;
	ciur();
	out << cnt;
	return 0;
}