var n,i,m,j:longint;
    a:array[1..2000001] of boolean;

begin

  assign(input,'ciur.in');
  assign(output,'ciur.out');
  reset(input);
  rewrite(output);

  read(n);

  for i:=2 to n do
    if a[i]=false then begin
      inc(m);
      j:=i*2;
      while j<=n do begin
        a[j]:=true;
        inc(j,i);
      end;
    end;

  write(m);
end.