#include <stdio.h>

#define NMAX 
int n; 
bool prime[NMAX];

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

	scanf("%d\n", &n);

	int primes = 0;	

	for (int i = 2; i <= n; i += 1)
		if (prime[i] == 0) {
			primes++;
			for (int j = i + i; j <= n; j += i) {
				prime[j] = 1;
			}
		}

	printf("%d\n", primes);

	return 0;
}