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 Rust (1.15.1) (judge verdict: Wrong Answer)

use std::io::*;
use std::str::FromStr;

pub fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

use std::cmp::min;

fn main() {
    let n = read::<usize>();
    let mut a = vec![0; n];
    let mut b = 0;
    let mut c = vec![0; n];
    for i in 0..n {
        a[i] = read::<i64>();
        b += a[i] - (i+1) as i64;
        c[i] += a[i] - (i+1) as i64;
    }
    if b % (n as i64) == 0 {
        b /= n as i64;
    } else {
        if b > 0 {
            b /= n as i64;
        } else {
            b = b.abs() / n as i64;
            b *= -1;
        }
    }

    let mut ans = vec![0; 5];
    for i in 0..n {
        ans[0] += (a[i] - ((b-2) + (i+1) as i64)).abs()
    }
    for i in 0..n {
        ans[1] += (a[i] - ((b-1) + (i+1) as i64)).abs()
    }
    ans[0] = min(ans[0], ans[1]);
    for i in 0..n {
        ans[2] += (a[i] - (b + (i+1) as i64)).abs()
    }
    ans[0] = min(ans[0], ans[2]);
    for i in 0..n {
        ans[3] += (a[i] - ((b+1) + (i+1) as i64)).abs()
    }
    ans[0] = min(ans[0], ans[3]);
    for i in 0..n {
        ans[4] += (a[i] - ((b+2) + (i+1) as i64)).abs()
    }
    ans[0] = min(ans[0], ans[4]);
    println!("{}", ans[0]);
}