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We all know the impressive story of Robin Hood. Robin Hood uses his archery skills and his wits to steal the money from rich, and return it to the poor. There are n citizens in Kekoland, each person ...

边界一定不能写成死循环。多画几次就能看出来的。

Given N numbers, X1, X2, ... ,XN, let us calculate the difference of every pair of numbers: ∣Xi- Xj∣ (1 ≤ i ＜ j ≤ N). We can getC(N,2) differences through this work, and now your task is to find