#include <cstdio>

using namespace std;

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

	int n, primesno = 0;
	scanf("%d", &n);
	bool is_prime[n+1];
	for(int i=0; i<=n; ++i)
		is_prime[i] = 1;

	for(int i=2; i<=n; ++i)
		if (is_prime[i])
			for(int j=i+i; j<=n; j = j + i)
				is_prime[j] = 0;

	for(int i=2; i<=n; ++i)
		primesno += is_prime[i];
	printf("%d\n", primesno);
	return 0;
}