#include <fstream>
#include <bitset>

using namespace std;

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

int ans;
bitset<2100000> isPrime;

int main() {
	int N;
	fin >> N;
	for (int i = 2; i <= N; ++i) {
		if (isPrime[i] == 0) {
			++ans;
			for (int j = i * i; j <= N; j += i) {
				isPrime[j] = 1;
			}
		}
	}

	fout << ans << '\n';
	fout.close();
	return 0;
}