#include <cstdio>

using namespace std;

int n, nr = 1;
char prime[2000005];

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

	scanf("%d", &n);
	fclose(in);

	for (int i = 3; i <= n; ++i) prime[i] = 1;

	for (int i = 3; i <= n; i += 2)
		if (prime[i]) {
			++nr;
			for (int j = 3 * i; j <= n; j += i << 1) prime[j] = 0;
		}

	printf("%d", nr);
	fclose(out);

    return 0;
}