#include <iostream>
#include <fstream>

int ciur(int n) {
	if (n <= 1)
		return 0;

	int ret = n - 1;

	int i, j;

	for (i = 4; i <= n; i += 2)
		--ret;

	for (i = 3; i * i <= n; i += 2) {
		for (j = i * i; j <= n; j += i << 1)
			--ret;
	}

	return ret;
}

int main() {			  
	std::ifstream fin("ciur.in");
	std::ofstream fout("ciur.out");

	int N;
	fin >> N;

	fout << ciur(N);

	fin.close();
	fout.close();

	return 0;
}