#include<iostream>
#include<fstream>
using namespace std;
int main()
{
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	int prim = 0, num, t = 0;
	f >> num;
	for (int i = 2; i <= num; ++i){
		for (int j = 2; j < i; ++j){
			if (i%j == 0)
				t++;
		}
		if (t==0)
			prim++;
		t = 0;
	}
	g << prim;
	f.close();
	g.close();
	return 0;
}