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: Time Limit Exceeded)

#include <stdio.h>
#include <stdlib.h>
void bubblesort(int a[],int n){
    int i,v;
    int flag=1;
    long long sum=0;
    while(flag){
        flag=0;
        for(i=n-1;i>0;i--){
            if(a[i]<a[i-1]){
                v=a[i];
                a[i]=a[i-1];
                a[i-1]=v;
                flag=1;
            }
        }
    }
    if(n%2==0){
        for(i=0;i<n;i++)
            sum+=abs(a[i]-a[n/2]);
    }
    else{
        for(i=0;i<n;i++)
            sum+=abs(a[i]-a[(n-1)/2]);
    }
    printf("%lld",sum);
    
}
        
int main(){
    int n;
    scanf("%d",&n);
    int i;
    int a[n],cpy[n];
    for(i=0;i<n;i++){
        scanf("%d",&cpy[i]);
        a[i]=cpy[i]-(i+1);
    }
    bubblesort(a,n);
}