Решение задачи ExamBegin9

uses PT4Exam;

var
  a, x: integer;
  num: boolean;

begin
  Task('ExamBegin9');
  ReadLn(a);
  x := 1; num := false;
  while x <= a do
  begin
    x := x * 2;
    if (x = a) or (a = 1) then num := true;
  end;
  if num = true then Write('YES')
  else Write('NO');
end.