#include <iostream>
#include <cmath>
using namespace std;

void count_Prime(int n);
int IsPrime(int num);


int main()
{
	int Data = 0;
	while (cin >> Data)
	{
		count_Prime(Data);
	}

	return 0;
}

void count_Prime(int n)
{
	int counter = 0,  i = 0;
	for (i = 2; i < n; ++i)
	{
		counter += IsPrime(i);		
	}

	cout << counter << endl;

}

int IsPrime(int num)
{
	if (num < 2) return 0;
	else if (num == 2) return 1;
	else if (num % 2 == 0) return 0; // ??¶??°????????????????????????

	double sqrtNum = sqrt(num);
	for (int i = 3; i <= sqrtNum; i += 2)
	{
		if (num % i == 0)
		{
			// ?´???°??§?????????
			return 0;
		}
	}

	// ?´???°??§??????
	return 1;
}