#include <fstream>

using namespace std;

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

int main()
{
	int numerePrime = 0, n;
	bool ok = false;
	f >> n;

	for (int i = 3; i <= n; i++)
	{
		ok = false;
		for (int j = 2; j <i / 2&& ok==false; j++)
		{
			if (i % j == 0)
				ok = true;
}
		if (ok == false)
			numerePrime++;
	 }
	g << numerePrime;

	return 0;

}