#include <stdio.h>

#define N 2000001

char not_prime[N];
int n, total;

void sift(int prime)
{
	int i;

	for (i = 3; i <= n / prime; i += 2)
		not_prime[i * prime] = 1;
}

int main()
{
	int i, nsqrt;

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

	scanf("%d", &n);

	total++;
	for (i = 3; i < n; i += 2)
		if (!not_prime[i]) {
			sift(i);
			total++;
		}

	printf("%d\n", total);
}