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: Wrong Answer)

#include <iostream>
#include <vector>
#include <cstdlib>
using namespace std;

int main()
{
    int sum = 0;
    int mid, max, min, b;
    int tmp, ans;

    int N;
    cin >> N;

    vector<int> A(N);
    for( int i = 0; i < N; ++i ){
        cin >> A[i];
        A[i] -= i + 1;
        sum += A[i];
    }

    mid = sum / N;
    max = mid + 2;
    min = mid - 2;

    for( b = min; b <= max; ++b ){
        tmp = 0;
        for( int i = 0; i < N; ++i ){
            tmp += abs(A[i] - b);
        }
        if( b == min ) ans = tmp;
        else if( tmp < ans ) ans = tmp;
        
        cout << b << " : " << tmp << endl;
    }

    cout << ans << endl;

    return 0;
}