#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 = 1; i <= n; ++i) prime[i] = 1;

	// prime[i] == 1 <=> 2 * i + 1 is prime

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

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

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

    return 0;
}