#include<fstream>

using namespace std;

bool a[2000001];

int main()
{
	int i, n, j, contor;
	
	ifstream fin("ciur.in");
	fin >> n;
	fin.close();
	
	for (i = 3; i * i <= n; i += 2)
		if (a[i] == false)
			for (j = i * i; j <= n; j = j + 2 * i)
				a[j] = true;
	
	contor = 1;
	for (i = 3; i <= n; i += 2)
		if (!a[i]) contor++;

	ofstream fout("ciur.out");
	fout << contor << "\n";
	fout.close();
	
	return 0;
}