package leetcode.test;

import java.util.Scanner;

public class Test3 {
 public static void main(String[] args) {
 Scanner in = new Scanner(System.in);
 int n = in.nextInt();
 int[] nums = new int[n];
 for (int i = 0; i < n; i++) {
 nums[i] = in.nextInt();
 }
 if (nums.length == 2 && nums[0]!=nums[1]) {
 System.out.println("-1");
 } else {
 int min = nums[0];
 int sum = min;
 int temp = min;
 for (int i = 1; i < n; i++) {
 sum += nums[i];
 min = Math.min(min, nums[i]);
 temp ^= nums[i];
 }
 if (temp!=0) {
 System.out.println("-1");
 } else {
 System.out.println(sum-min);
 }
 }
 }
}