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<cmath>
#include<algorithm>
using namespace std;
int main()
{
    int n, a;
    vector<int> b;
    cin >> n;
    for(int i = 1; i <= n; i++){
        cin >> a;
        b.push_back(a - i);
    }
    sort(b.begin(), b.end());
    int med = (b[(b.size()-1)/2] + b[(b.size()-1) - (b.size()-1)/2]) / 2;
    int ans = 0, ans2 = 0, ans3 = 0;
    for(int i = 0; i < b.size(); i++){
        ans += abs(b[i] - med);
        ans2 += abs(b[i] - med - 1);
        ans3 += abs(b[i] - med + 1);
    }
    cout << min(ans, min(ans2, ans3)) << endl;
    return 0;
}