#include <iostream>
#include <fstream>
#include <cmath>


using namespace std;


int N;
bool neprim[2000000];
ifstream in ("ciur.in");
ofstream out("ciur.out");


int main()
{	
	int i, nr = 0, aux = 0;
	in >> N;
	for(i = 2; i <= N; i++)
	{
		if(!neprim[i])
		{
			nr++;
			aux = 2 * i;
			while(aux <= N)
			{
				neprim[aux] = true;
				aux = aux + i;
			}
		}
	}
	cout << nr << "\n";
	out << nr;

	return 0;
}