#include <bitset>
#include <fstream>

using namespace std;

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

const int NMAX = 2000000;

bitset<NMAX + 5> b;
int n, i, j;

int main()
{
	fin >> n;
	for (i = 3; i * i <= n; i += 2)
		if (!b[i])
			for (j = i * i; j <= n; j += i << 1)
				b[j] = true;
	fout << ((n + 1) >> 1) - b.count();
	fin.close();
	fout.close();
	return 0;
}