Sonya and Problem Wihtout a Legend

给定一个有 $n$ 个正整数的数组，一次操作中，可以把任意一个元素加一或减一。（元素可被减至负数或 $0$），求使得原序列严格递增的求最小操作次数。

Sonya was unable to think of a story for this problem, so here comes the formal description. You are given the array containing $ n $ positive integers. At one turn you can pick any element and increase or decrease it by $ 1 $ . The goal is the make the array strictly increasing by making the minimum possible number of operations. You are allowed to change elements in any way, they can become negative or equal to $ 0 $ .

The first line of the input contains a single integer $ n $ ( $ 1<=n<=3000 $ ) — the length of the array. Next line contains $ n $ integer $ a_{i} $ ( $ 1<=a_{i}<=10^{9} $ ).

Print the minimum number of operation required to make the array strictly increasing.

7
2 1 5 11 5 9 11

9

5
5 4 3 2 1

12

In the first sample, the array is going to look as follows: $ 2 $ $ 3 $ $ 5 $ $ 6 $ $ 7 $ $ 9 $ $ 11 $ $ |2-2|+|1-3|+|5-5|+|11-6|+|5-7|+|9-9|+|11-11|=9 $ And for the second sample: $ 1 $ $ 2 $ $ 3 $ $ 4 $ $ 5 $ $ |5-1|+|4-2|+|3-3|+|2-4|+|1-5|=12 $