#include <iostream>
#include <fstream>

using namespace std;

int main()
{
	ifstream in("ciur.in");
	ofstream out("ciur.out");

	int nr_prime = 0, nr;
	bool prime[2000003];

	in >> nr;

	for (int i = 2; i < nr; i++)
		prime[i] = true;

	for (int i = 2; i < nr; i++)
	if (prime[i] == true)
	{
		nr_prime++;
		for (int j = i + i; j < nr; j = j + i)
			prime[j] = false;
	}

	out << nr_prime;
}