Question:

MEX Problem

Given an array arr contalning n non-negative integers and an element x, in one operation, x can be added to or subtracted from any element of the array. MEX of an array is defined as the smallest non-negative integer which is not present in the array. For example, the MEX of [0, 1, 1, 3] is 2, and the MEX of [1, 2, 4] is 0.

Find the maximum possible MEX of the array that can be achieved by doing the above operation any number of times.