#include<fstream>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int prim(int a)
{
	int d;
	if(a == 0 || a == 1)
		return 0;
	if(a == 2)
		return 1;
	for(d = 3; d * d <= a; d++)
		if(a % d == 0)
			return 0;
		return 1;
}
int main()
{
	int n, nrpr = 0;
	fin >> n;
	for(int i = 2; i <= n ; i++)
		if(prim(i) == 1)
			nrpr++;
	fout << nrpr;
	fin.close();
	fout.close();
	return 0;
}