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

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

int isPrime(int N) {
	for (int d = 2; d * d <= N; ++d) {
		if (N % d == 0) {
			return 0;
		}
	}
	return 1;
}

int main() {
	int N, nr = 0, i = 1;
	f >> N;
	while (i <= N) {
		if (isPrime(i) == 1) {
			nr++;
		}
		i += 2;
	}
	g << nr;
	return 0;
}