#include <cstdio>
#include <bitset>
#include <vector>
using namespace std;
const int NMAX = 2000505;
int N;
vector<int> pr;
short int lp[NMAX];

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

	scanf("%d", &N);
	for (int i = 2; i <= N; i++) {
		if (lp[i] == 0) {
			lp[i] = i;
			pr.push_back(i);
		}

		for (int j = 0; j < pr.size() && pr[j] <= lp[i] && i * pr[j] <= N; j++) {
			lp[i * pr[j]] = pr[j];
		}
	}

	printf("%d\n", (int) pr.size());
	return 0;
}