#include <cstdio>
#include <bitset>
using namespace std;
const int NMAX = 2000505;
bitset<NMAX> mark;
int N;

int main() {
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	scanf("%d", &N);
	for (int i = 2; i * i <= N; i++) {
		if (!mark[i]) {
			for (int j = i * i; j <= N; j += i) {
				mark[j] = 1;
			}
		}
	}

	printf("%d\n", N - 1 - mark.count());
	return 0;
}