#include <cstdio>
#include <queue>
#include <cstring>

using namespace std;

inline int next_int() {
	int d;
	scanf("%d", &d);
	return d;
}

bool P[2000001];

int main() {
	//freopen("ciur.in", "r", stdin);
	//freopen("ciur.out", "w", stdout);
	int n = next_int();
	for (int i = 2; i * i <= n; i++) {
		if (P[i] == 0) {
			for (int j = i * i; j <= n; j += i) {
				P[j] = 1;
			}
		}
	}
	int ans = 0;
	for (int i = 2; i <= n; i++) {
		if (P[i] == 0) {
			ans++;
		}
	}
	printf("%d", ans);
	return 0;
}