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 <stack>
#include <map>
#include <algorithm>
#include <queue>
#include <math.h>
#include <string.h>

using namespace std;

// NG

int N;
int a[1000000];
int c[1000000];

long loss(long k) {
    long l;
    for (int i=1; i <= N; i++) {
        l += abs(c[i] - k);
    }
    return l;
}
int main(int argc, char** argv) {
    cin >> N;
    for (int i=1; i <= N; i++) cin >> a[i];
    for (int i=1; i <= N; i++) c[i] = a[i] - i;
    sort(&c[1], &c[1] + N);
    //for (int i=1; i <= N; i++) cout << c[i] << endl;;

    long i = N / 2 + 1;
    long ans = loss(c[i]);
    ans = min(ans, loss(c[i - 1]));
    ans = min(ans, loss(c[i + 1]));
    cout << ans << endl;
}