# include <algorithm>

using namespace std;

int n,k;
char a[2000005];

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d", &n);
	fill(a+2,a+n+2,1);
	for (int i=2;i<=n;i++)
		if (a[i])
		{
			k++;
			for (int j=2*i;j<=n;j+=i)
				a[j]=0;
		}
	printf("%d", k);
	return 0;
}