import math


def percentile(values, k):
    """Find the percentile of a list of values.

    :param list values: The list of values to find the percentile of
    :param int k: The percentile to find
    :rtype: float or int

    """
    if not values:
        return None
    values.sort()
    index = (len(values) * (float(k) / 100)) - 1
    return values[int(math.ceil(index))]