def common(l1: list, l2: list):
    ret = set()
    for e1 in l1:
        for e2 in l2:
            if e1 == e2:
                ret.add(e1)
    return sorted(list(ret))
from typing import List
def mean_absolute_deviation(numbers: List[float]) -> float:
    mean = sum(numbers) / len(numbers)
    return sum(abs(x - mean) for x in numbers) / len(numbers)