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++14 (GCC 5.4.1) (judge verdict: Time Limit Exceeded)

#include <iostream>
using namespace std;

int abs(int a, int b, int c){
    int ret = a - (b + c);
    if(ret < 0){
        return -ret;
    }else{
        return ret;
    }
}

int main(){
    int n;
    cin >> n;
    int a[n+1];
    for(int i = 1;i <= n;i++){ cin >> a[i]; }
    int max = 0;
    for(int i = 1;i <= n;i++){
        if(max < abs(a[i],0,i)) max = abs(a[i],0,i);
    }

    int ret = 1000000000;
    for(int b = -max;b <= max;b++){
        int s = 0;
        for(int i = 1;i <= n;i++){
            s += abs(a[i], b, i);
        }
        if(s < ret){
            ret = s;
        }
    }
    cout << ret << endl;
    return 0;
}