#include <iostream>
#include <fstream>

std::ifstream infile("ciur.in");
std::ofstream outfile("ciur.out");

bool prim(int n)
{
	int d = 2;
	while (d * d <= n)
	{
		if (n % d == 0)
			return false;
		d++;
	}

	return true;
}

int main()
{
	int n;
	int c = 0;
	infile >> n;

	for (int i = 2; i < n; i++)
	{
		if (prim(i))
			c++;
	}

	outfile << c;
}