说明：  本程序实现十字路口交通灯的模拟控制。假设有一个十字路口，分为南北路口和东西路口。十字路口交通灯的变化规律要求： （1） 南北路口的绿灯、东西路口的红灯同时亮30秒，并且显示倒计时。 （2） 南北路口的黄灯闪烁若干次，同时东西路口的红灯继续亮。 （3） 南北路口的红灯、东西路口的绿灯同时亮20秒，并且显示倒计时。 （4） 南北路口的红灯继续亮、同时东西路口的黄灯亮闪烁若干次。 （5） 转（1）重复。 若键盘输入“R”则返回DOS，结束程序。
(This procedure realize at the crossroads of the analog control traffic lights. Assuming that there is a crossroads, divided into north and south and east-west road junctions junctions. Traffic lights at the crossroads of the changes of requirements: (1) the green light at the junction of North and South, East and West at the junction of the red light at the same time 30 seconds, and shows the countdown. (2) North and South at the junction of several blinking yellow light, while things continue to light the red light intersection. (3) red lights at the junction of North and South, East and West at the junction of bright green light at the same time 20 seconds, and shows the countdown. (4) north-south junction of the red light continues to shine, at the same time things blinking yellow light at the junction of several. (5) to (1) repeat. If the keyboard input )