#include <fstream>
#include <vector>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
	int N;
	in >> N;
	vector<bool> is_prime(N + 1, true);
	for (int i = 2; i <= N; i++)
	{
		if (is_prime[i])
		{
			for (int j = 2 * i; j <= N; j += i)
				is_prime[j] = false;
		}
	}
	int count = 0;
	for (int i = 2; i <= N; i++)
	{
		if (is_prime[i]) count++;
	}
	out << count;
	out.close();
	in.close();
}