#include<fstream.h>
long int n,prim[10000],i,j,nr,contor;
int main()
{
ifstream in("ciur.in");
ofstream out("ciur.out");
in>>n;
for(i=2;i<=n;i=i+1)
prim[i]=1;
for(i=2;i<=n;i=i+1)
if(prim[i]==1)
	       {for(j=i+i;j<=n;j=j+i)
		prim[j]=0;
		contor=contor+1;
		}
out<<contor;
in.close();
out.close();
return 0;
}