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 below_zero(operations: List[int]) -> bool:
    balance = 0
    for op in operations:
        balance += op
        if balance < 0:
            return True
    return False