function MonthDay(){
	var month = document.getElementById("month");
	var day   = document.getElementById("day");
	if(month.value!=0){
		day.disabled = false;
	}else{
		day.disabled = true;
	}
	
}

function DayDisable(){
  var month = document.getElementById("month");
  var day   = document.getElementById("day");
  
  
  if(day.value!=0 || month.value!=0){
  	day.disabled = false;
  }else{
    day.disabled = true;
  }
}

window.onload = DayDisable;