#include<fstream.h>
#include<math.h>
char v[4000100];
int main()
{
	bool gasit;
	int nn,t,a,b,d,c,i,n,nr=1;
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	f>>n;
	nn=sqrt(n);
	d=3;
	while(d<=n)
	{
		nr++;
		if(d<=nn)
		{
			a=d*d;
			b=(d<<1);
			while(a<=n)
			{
				c=(a>>1);
				if(!v[c])
					v[c]=1;
				a+=b;
			}
		}
		gasit=0;
		c=(d>>1)+1;
		while(!gasit)
		{
			if(!v[c])
			{
				d=(c<<1)+1;
				gasit=1;
			}
			else c++;
		}
	}
	g<<nr;
	return 0;
}