#include <iostream>
#include <fstream>
//#include "definitions.h"

using namespace std;


bool isPrimeNumber(int n) {
	for (int i = 2; i<=n/2; i++) 
		if (n%i == 0) return false;
	return true;
}

int countPrimes(int n) {
	int count = 0;
	for (int i = 2; i < n; i++) {
		if (isPrimeNumber(i)) {
			count++;
		}
	}
	return count;
}

int main() {
	ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n;
    f>>n;
	g<<countPrimes(n);
	return 0;
}