#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

	vector<bool> p;

	int n;
	in >> n;


	p.resize(n, false);

	int total = 1;
	for ( int i = 3; i < n; i += 2 )
		if (!p[i])
		{
			++total;

			for ( int j = 2; i*j < n; j++ )
			{
				p[i*j] = true;
			}
		}

	out << total << "\n";

	return 0;
}