#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()
{
	int n;
	cin >> n;
	int count = 0;
	for (int i = 1; i <= n; i++)
		if (isPrime(i))
			count++;
	cout << count << endl;
}
