定时减法计数。输入数据0到9之间三位数，开始计时，每秒减一。当计数完成时，可做二次开发。还可做简单加减法-Timing counts subtraction. Input data between the three-digit 0-9, start running, by one per second. When the count is complete, do the secondary development. Also to do simple addition and subtrac