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 Kotlin (1.0.0) (judge verdict: Accepted)

fun main(args: Array<String>) {
    val N = nextInt()
    val A = listOfInt()
    val B = A.mapIndexed { index, v -> v - (index + 1) }.sorted()
    val b = B[N / 2]
    val ans = A.withIndex().sumByLong { Math.abs(it.value - (b + it.index + 1)).toLong() }
    println(ans)
}
inline fun <T> Iterable<T>.sumByLong(selector: (T) -> Long): Long {
    var sum = 0L
    for (element in this) sum += selector(element)
    return sum
}
fun next() = readLine()!!
fun nextInt() = Integer.parseInt(next())
fun nextInt(offset: Int = 0) = nextInt() + offset
fun listOfString() = next().split(" ")
fun listOfInt() = listOfString().map { Integer.parseInt(it) }
fun listOfInt(offset: Int = 0) = listOfString().map { Integer.parseInt(it) + offset }