//============================================================================
// Name        : CiurEr.cpp
// Author      : Lucian
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <fstream>
using namespace std;

int main() {
	ifstream f("ciur.in");
	ofstream g("ciur.out");

	unsigned n,i,j,k=0;
	f>>n;

	char prim[2000001];
	for (i = 2; i <= n; ++i)
	        prim[i] = 1;
	for (i = 2; i <= n; ++i)
		if (prim[i])
	        {
	            ++k;
	            for (j = i+i; j <= n; j += i)
	                prim[j] = 0;
	        }

	g<<k;


	f.close();
	g.close();

	return 0;
}