#include <fstream>

using namespace std;

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

const int Nmax = 2000005;
int n, cnt;
bool prim[Nmax];

int main()
{
	fin >> n;
	for (int i = 2; i <= n; ++i)
		prim[i] = 1;
	for (int i = 2; i <= n; ++i)
	{
		if (prim[i])
		{
			++cnt;
			for (int j = i + i; j <= n; j += i)
				prim[j] = 0;
		}
	}
	fout << cnt << '\n';
	fin.close();
	fout.close();
	return 0;
}