To check if a virtual counter such as c is equal to zero, just divide the real counter by 5, see what the remainder is, then multiply by 5 and add back the remainder.
要检查一个虚拟计数器比如 c 是否等于零，只要把实际计数器除以 5，看余数是什么，接着乘以 5 并加回余数。