#include <fstream>
#include <bitset>

const int MAX_SIZE(1000001);

std::bitset<MAX_SIZE> Mark;

int main (void)
{
	std::ifstream input("ciur.in");
	int n;
	input >> n;
	input.close();
	n /= 2;
	int counter(1);
	for (int i(1) ; i <= n ; ++i)
		if (!Mark[i])
		{
			++counter;
			for (int j(i), k(2 * i) ; j <= n ; j += k)
				Mark[j] = true;
		}
	std::ofstream output("ciur.out");
	output << counter << '\n';
	output.close();
	return 0;
}