#include <fstream>
using namespace std;
char v[2000005];
int main()
{
	int n, nr = 1;
	ifstream cin("ciur.in");
	ofstream cout("ciur.out");
	cin >> n;
	for (int i = 3; i <= n; i += 2)
	if (v[i] == 0)
	{
		nr++;
		for (int j = 3 * i; j <= n; j += 2 * i)v[j] = 1;
	}
	cout << nr;
	return 0;
}