#include <iostream>

using namespace std;

int main(void)
{
	int n;
	int pnum;
	
	while (cin >> n){
		int ct  = 0;
		for (int i = 2; i <= n; i++){
			for (pnum = 2; pnum <= n; pnum++){
				if (i % pnum == 0){
					break;
				}
			}
			if (i == pnum){
				ct++;
			}
		}
		cout << ct << endl;
	}
	
	return (0);
}