#include<iostream>
#include<fstream>

#define Nmax 2000001

using namespace std;

int main() {
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	long N;
	long nr = 0;
	f >> N;
	bool V[Nmax];
	for ( int i = 2; i <= N; i++ ) {
		V[i] = true;
	}
	for ( int i = 2; i <= N; i++ ) {
		if ( V[i] ) {
			nr ++;
			for ( int j = i + i; j <= N; j += i ) {
				V[j] = false;
			}
		}
	}
	g << nr;
	f.close();
	g.close();
	return 0;
}