import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        int[] arr = new int[n];
        StringTokenizer st = new StringTokenizer(br.readLine());

        for (int i = 0; i < n; i++) {
            arr[i] = Integer.parseInt(st.nextToken());
        }

        long bullet = 0;
        for (int i = 0; i < n / 2; i++) {
            bullet += Math.abs(arr[i] - arr[n - i - 1]);
        }

        System.out.println(bullet);
    }
}