#include <math.h>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
	int n,i,d,prim,k=0;
f>>n;
for (i=2;i<=n;i++)
{
	d=2;
	prim=1;
while ((d<=sqrt(i))&&(prim==1))
	{
		if (i%d==0)
			prim=0;
		else
			d=d+1;
	}
if (prim==1)
	k=k+1;
}
g<<k<<"\n";
}