#include<iostream>
#include<cmath>
using namespace std;
bool isPrime(int x)
{
	if (x < 2)
		return false;
	if (x == 2)
		return true;
	if (x % 2 == 0)
		return false;
	for (int i = 3; i <= (int)sqrt(x); i+=2)
		if (x%i == 0)
			return false;
	return true;
}
int main()
{
	while (true)
	{
		int n;
		cin >> n;
		if (cin.fail())
			break;
		int count = 0;
		for (int i = 1; i <= n; i++)
			if (isPrime(i))
				count++;
		cout << count << endl;
	}
}
