There is a staircase in a certain toy city. There are about dozens of steps, but certainly less than one hundred. The four children Akesai, Barton, Kelin and Dupont play games together. After the game starts, if the same step is stepped on four times, the step will turn red; step on three times, it will turn yellow; step on it twice, it will turn green; step on it once, it will turn blue. Kesai went down 2 steps in one step, Patton went down 3 steps in one step, Kelin went down 4 steps in one step, and DuPont was the most capable, he could go down 5 steps in one step. Come down and find that the red steps are only at the highest and lowest. How many blue steps are there on the staircase now?
某玩具城有一楼梯，大约有几十级，但肯定不到一百级．四位小朋友阿克赛，巴顿、克林、杜邦一起玩游戏．游戏开始后，若同一级台阶被踩四下，则台阶呈红色；踩三下，则呈黄色；踩二下，则呈绿色；踩一下，则呈蓝色，若四人下楼梯时，阿克赛一步下2级台阶，巴顿一步下3级台阶，克林一步下4台阶，而杜邦的本事最大，竟然一步能下5台阶．下来发现，呈红色的台阶仅在最高处和最低处．现在楼梯上呈蓝色的台阶有多少级．
<result>20</result>