#include <fstream>

using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
bool a[1001];
int N;
int Ciur()
{
for (int i = 3; i * i < N; i = i + 2)
{
	if (a[i] == 0)
		for (int j = i * i; j < N; j = j + 2 * i)
{
a[j] = i;
}
	}

	int prime[10000];
	int cnt=1;

	for (int i = 3; i < N; i = i + 2)
	{
		if (a[i] == 0)
		{

			cnt++;
		}
	}
	return cnt;
}

int main()
{
	cin >> N;
	cout<<Ciur();


}