/*
 * ciur.cpp
 *
 *  Created on: Nov 5, 2008
 *      Author: stefan
 */

#include <iostream>
#include <vector>
#include <stdio.h>

using namespace std;

int main()
{
	vector<bool> prim;
	long int n, count;

	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	cin >> n;

	prim.resize((count = n)+1, true);

	for (long int i = 2; i < n; ++i)
		if (prim[i])
			for (long int j = 2*i; j <= n; j+=i)
			{
				if(prim[j])
				{
					prim[j] = false;
					--count;
				}
			}

	cout << count-1;

	return 0;
}