////TIP To <b>Run</b> code, press <shortcut actionId="Run"/> or
//// click the <icon src="AllIcons.Actions.Execute"/> icon in the gutter.
//void main() {
//    //TIP Press <shortcut actionId="ShowIntentionActions"/> with your caret at the highlighted text
//    // to see how IntelliJ IDEA suggests fixing it.
//    IO.println(String.format("Hello and welcome!"));
//
//    for (int i = 1; i <= 5; i++) {
//        //TIP Press <shortcut actionId="Debug"/> to start debugging your code. We have set one <icon src="AllIcons.Debugger.Db_set_breakpoint"/> breakpoint
//        // for you, but you can always add more by pressing <shortcut actionId="ToggleLineBreakpoint"/>.
//        IO.println("i = " + i);
//    }
//}


import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

//        int m = sc.nextInt();

        int[] arr = new int[n];
        for (int i=0; i<n; i++){
            arr[i]=sc.nextInt();
        }

        int bullet =0;
       for (int i=0;i<n/2;i++){
           if(arr[i]>arr[n-i-1]){
               bullet+= arr[i]-arr[n-i-1];
           }
           else{
               bullet+= arr[n-i-1]-arr[i];
           }
       }

       System.out.print(bullet);
    }
}