Problem:
Score : 300 points

Problem Statement

Snuke has an integer sequence A of length N.

He will freely choose an integer b.
Here, he will get sad if A_i and b+i are far from each other.
More specifically, the sadness of Snuke is calculated as follows:

abs(A_1 - (b+1)) + abs(A_2 - (b+2)) + ... + abs(A_N - (b+N))

Here, abs(x) is a function that returns the absolute value of x.

Find the minimum possible sadness of Snuke.

Constraints

1 \leq N \leq 2 \times 10^5

1 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the minimum possible sadness of Snuke.

Sample Input 1

5
2 2 3 5 5

Sample Output 1

2

If we choose b=0, the sadness of Snuke would be abs(2-(0+1))+abs(2-(0+2))+abs(3-(0+3))+abs(5-(0+4))+abs(5-(0+5))=2.
Any choice of b does not make the sadness of Snuke less than 2, so the answer is 2.

Sample Input 2

9
1 2 3 4 5 6 7 8 9

Sample Output 2

0

Sample Input 3

6
6 5 4 3 2 1

Sample Output 3

18

Sample Input 4

7
1 1 1 1 2 3 4

Sample Output 4

6

Solution in PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
// C
fscanf(STDIN, '%d', $n);
$a = array_map('intval', explode(' ', trim(fgets(STDIN))));
for ($i = 0; $i < $n; $i++) $aa[] = $a[$i] - ($i + 1);
$b = round(array_sum($aa) / $n);
$ans = PHP_INT_MAX;
for ($i = $b - 1; $i <= $b + 1; $i++) {
    $cnt = 0;
    for ($j = 0; $j < $n; $j++) $cnt += abs($a[$j] - ($j + 1) - $i);
    $ans = min($ans, $cnt);
}
echo $ans;