#include <fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
int main()
{
	int n, s,ok=1;
		cin >> n;
		for (int i = 2; i <= n; i++)
			for (int z = 2; z <= i / 2; z++) if (i % z == 0) ok=0;
			if (ok == 1) s++;
		cout << s;

}