def merge_sort(arr):
    # If the array length is less than 2, no sorting is needed
    if len(arr) <= 1:
        return arr

    # Find the middle of the array
    mid = len(arr) // 2

    # Divide the array into two halves
    left_half = merge_sort(arr[:mid])
    right_half = merge_sort(arr[mid:])

    # Merge two sorted halves
    return merge(left_half, right_half)


def merge(left, right):
    result = []
    i = j = 0

    # As long as there are elements left in both lists
    while i < len(left) and j < len(right):
        if left[i] <= right[j]:
            result.append(left[i])
            i += 1
        else:
            result.append(right[j])
            j += 1

    # Add the remaining elements (one of the lists may run out early)
    result.extend(left[i:])
    result.extend(right[j:])
    return result


# Example:

nums = [5, 2, 4, 6, 1, 3]
print("Before sorting:", nums)

nums = merge_sort(nums)
print("After sorting:", nums)