#include <cstdio>
#include <math.h>

using namespace std;

int main()
{
	int n,ct=0;
	bool prim;
	freopen("prime.in","r",stdin);
	freopen("prime.out","w",stdout);
	scanf("%d",&n);
	if (n>=1)
		ct++;
		//printf("%d ",1);
	if (n>=2)
		ct++;
		//printf("%d ",2);
	if (n>2)
		for (int i=3;i<=n;i=i+2)
		{	
			prim=true;
			for (int j=2;j<=sqrt(i)&&prim;j++)
				if (i%j==0)
					prim=false;
			if (prim)
				ct++;
				//printf("%d ",i);
		}
	printf("%d\n",ct-1);
	return 0;	
}