The main hall of UESTC is far from the dormitory. However, poor Hongshu has to go
there every day to talk with his teachers. This is the most unhappy thing on the
earth. However, Hongshu is so optimistic that he still digs a lot of fun during
that boring period.
There is a long flagstone walk on the way from the dormitory to the main hall.
This flagstone walk has N lines and four flagstones arranged in each line.
Hongshu always start from rightmost flagstone of the first line. In order to make
this walk funny, he would always step onto the left or right flagstone in the
next line if there is. For example, if Hongshu stands at the second rightmost
flagstone of the third line, he would choose to step to the first or third
rightmost one of the forth line. Note that Hongshu has only one choice when he is
at the corner of one line.
Because Hongshu has to go to the main hall every day, he wants to know how many
different ways to step across the flagstone walk. Can you help him?