program ciur;
type vector=array[1..20000] of 0..1;
var f,g:text;
    prim:vector;
    n,i,j,contor:word;
begin
 {    assign(f,'ciur.in');
     assign(g,'ciur.out');
     reset(f);
     rewrite(g);}
     read(n);
     contor:=0;
     for i:=2 to n do
     prim[i]:=1;
     for i:=2 to n do
     begin
          if (prim[i]=1) then
                             begin
                                  inc(contor);
                                  for j:=i+i to j do
                                  begin
                                       prim[j]:=0;
                                       j:=j+i-1;
                                  end;
                             end;
      end;
      write(contor);
{      close(f);
      close(g); }
end.