def find_missing_number(numbers):
    """
    akes a shuffled list of unique numbers from 1 to n with one element missing (which can be any number including n).
    :param numbers: array of intergers.
    :return: this missing number.
    """
    total = 1
    for i in range(2, len(numbers) + 2):
        total += i
        total -= numbers[i - 2]
    return total