// Galatan Tudor - Ion Luca High School
// Husi, Romania, Su, August 30, 2015

#include <fstream>

using namespace std;

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

bool sieve[2000001];
int n, i, j, ct;

int main ()
{
	in >> n;
	for (i=2; i<=n; i++)
	{
		if (sieve[i] == 0)
		{
			ct++;
			for (j=i*2; j<=n; j=j+i)
				sieve[j] = 1;
		}
	}
	out << ct;
	return 0;
}