某汽车轮渡口，过江渡船每次能载 10 辆车过江。过江车辆分别为客车类和
货车类，上船有如下规定：同类车先到先上船，客车先于货车上渡船，且每上 4 辆客车，才允许上一辆货车；若等待客车不足4辆则以货车代替；若无货车等待则允许客车都上船。(A car ferry ferry, river crossing boat, each time you can carry 10 vehicles across the river. The vehicles passing through the river are buses and buses respectively
The truck, on board the following provisions: first vehicle to go first, the bus before the truck ferry, and every 4 passenger cars are allowed on a truck; if waiting for the bus less than 4 in the truck instead; if there is no vehicle waiting for the bus are allowed on board.)