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 Lua (Lua 5.3.5) (judge verdict: Accepted)

local n=io.read("n")
local a={}
for i=1,n do
    a[i]=io.read("n")-i
end
table.sort(a)

if n%2==1 then
    local median=a[n//2+1]
    local sadness=0
    for i=1,n do
        sadness=sadness+math.abs(a[i]-median)
    end
    print(sadness)
else
    local median1=a[n//2]
    local sadness1=0
    local median2=a[n//2+1]
    local sadness2=0
    for i=1,n do
        sadness1=sadness1+math.abs(a[i]-median1)
        sadness2=sadness2+math.abs(a[i]-median2)
    end
    print(math.min(sadness1,sadness2))
end