Given an array of n integers and a number k, find the maximum number of elements whose sum is less than k, and return their sum.

To find the maximum number of elements whose sum is less than k, first sort the array in ascending order. Then, iterate through the sorted array, accumulating the sum and counting the elements. Stop when adding the next element would exceed k. The accumulated sum at that point is the answer. This approach has a time complexity of O(n log n) due to sorting and a space complexity of O(1) if sorting is done in-place, or O(n) otherwise.