#include <cstdio>
#include <cmath>

using namespace std;

bool prime[2000005];

// 1 - daca nu este prim
// 0 - daca este prim

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

	int N;

	scanf("%d", &N);


	prime[1] = 1;
	int counter = 0;

	for (int i = 2;i * i <= N;i ++) {
		if (!prime[i]) {
			for (int j = i + i;j <= N;j += i) {
				prime[j] = 1;
			}
		}
	}

	for (int i = 1;i <= N;i ++)
		if (!prime[i])
			counter ++;

	printf("%d", counter);
	return 0;
}