>  题目修改汇总：
>  A balls  
>   范围  0 <= n < 16 --> 0 <= n <= 16
>   all the balls are numbered from 1 to n --> all the balls are numbered from 1 to m
>   在html里面已改过，但在pdf里没有改。 
>    
> D firing range
>   output:
>   standing for the number of arcs which weren't covered by fire --> 
>    standing for the number of arcs which were covered by fire k times.
> 
>    (-109<=li<ri<=109, li<m) --> (-109<=li<=ri<=109, 0<=li<m)
> 
> and data like (300, 560) won't appear(because (300,560) = (300,200), li > ri is invalid).   -->
> and if a data like (300, 200) appears， that means this arc is like 300->0->200,  not 200->300.
> 即：跨0度的弧是会存在的。
> 
>   之前题目里有对k的描述。
> 
F msn
Di = abs (Ci – Si)  --> Di = abs (Cj – Si)