#include<fstream>
#include<climits>
using namespace std;

const int nMSize = 2000001;

bool numbers[nMSize];

int main() {
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	int N;
	in >> N;
	int s = 0;
	for (int i = 2;i <= N;++i) {
		if (!numbers[i]) {
			s++;
			for (int j = i; i*j <= nMSize;++j)
				numbers[i*j] = true;
		}
	}
	out << s;
}