#include <iostream>
#include <bitset>
#include <string.h>
#include <fstream>

using namespace std;

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

int NumerePrime(int limitaSup)
{
	bitset<2000001> prim;
	prim.set();
	int contor = 0;

	for (int i = 2; i <= limitaSup; i++)
		if (prim[i])
		{
			contor++;
			int mult = i * 2;
			while (mult <= limitaSup)
			{
				prim[mult] = 0;
				mult += i;
			}
		}
	return contor;
}


int main()
{
	int n;
	fin >> n;
	fout << NumerePrime(n);
}