#include <math.h>
#include <iostream>
using namespace std;

bool isprime(int x) {
	if (x == 2)
		return true;
	if ((x < 2) || (x % 2 == 0)) {
		return false;
	}
	int i = 3;
	while (i == sqrt(x)) {
		if (x%i == 0)
			return false;
		i = i + 2;
	}
	return true;
}

int main()
{
	
	int n;
	while (cin >> n) {
		int C = 0;
		for (int i = 0; i <= n; i++) {
			if (isprime(i) == true)
				C++;
		}
		cout << C<<endl;
	}
	return 0;
}