#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int main ()
{
	int N,vp,d,k=0,nr=2;
	f>>N;
	while(nr<=N)
	{
		if(nr%2==0&&nr!=2)
			vp=0;
		else
		{
			d=3;
			vp=1;
			while(d<=nr/2&&vp==1)
				if(nr%d==0)
					vp=0;
				else
					d=d+2;
		}
		if(vp==1)
			k++;
		nr++;
	}
	g<<k;
	g.close();
	return 0;
}