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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<math.h>
int main()
{
    int n;
    scanf("%d", &n);
    int a[200005];
    int i;
    for (i = 0; i < n; i++)
    {
        scanf("%d", &a[i]);
        a[i] -= i - 1;
    }
    int x;
    for (i = 0; i < n - 1; i++)
    {
        if (a[i] > a[i + 1])
        {
            x = a[i];
            a[i] = a[i + 1];
            a[i + 1] = x;
            if (i > 0)
                i -= 2;
        }
    }
    int j;
    int b;
    int ans = 0;
    if (n % 2 == 0)
    {
        b = a[n / 2];
        for (i = 0; i < n; i++)
            ans += abs(a[i] - b);
    }
    else
    {
        int x = 0;
        b = a[n / 2];
        for (i = 0; i < n; i++)
            ans += abs(a[i] - b);
        b = a[(n / 2) + 1];
        for (i = 0; i < n; i++)
            x += abs(a[i] - b);
        if (ans > x)
            ans = x;
    }
    printf("%d\n", ans);
    return 0;
}