Maximum Difference Sum

Ramanujan is a Mathematician. One day when he was looking for a book in library, he came across a book named Formule Di Matematica. He found it interesting and started reading it. While going through the book, he found a function D which was as following: D(1,a2,a3,..,an >) = |a1-a2| + |a2-a3| + ... +|an-1-an| where 1,a2,a3,...,an > is a sequence of n distinct integers. Ramanujan quickly unders