#include <fstream>

#include <vector>

using namespace std;

ifstream fin ("ciur.in");

ofstream fout ("ciur.out");

void ciur (int n, vector <bool> & prim, vector <int> & v) {

	prim[0] = prim[1] = false;

	for (int i = 2; i * i <= n; ++i)
		if (prim[i])
			for (int j = i * i; j <= n; j += i)
				prim[j] = false;

	for (int i = 2; i <= n; ++i)
		if (prim[i])
			v.push_back (i);
}

int main () {

	int n;

	fin >> n;

	vector <bool> prim (n + 1, true);

	vector <int> v;

	ciur (n, prim, v);

	fout << v.size ();

	return 0;
}