class Attraction:
    def __init__(self, satis: int, waiting: int) -> None:
        self.satisfied = satis
        self.waiting = waiting

    def visited(self):
        self.satisfied //= 2

    @property
    def satis_per_h(self) -> float:
        return self.satisfied / self.waiting


def main():
    T = int(input())
    N = int(input())
    c = list(map(int, input().split()))
    v = list(map(int, input().split()))

    attractions = [Attraction(satis, waiting) for satis, waiting in zip(v, c)]
    attractions = list(filter(lambda att: att.waiting <= T, attractions))
    sum_satisfied = 0

    while attractions:
        attractions.sort(key=lambda att: att.satis_per_h)
        sum_satisfied += attractions[-1].satisfied
        attractions[-1].visited()
        T -= attractions[-1].waiting
        attractions = list(filter(lambda att: att.waiting <= T, attractions))

    print(sum_satisfied)


if __name__ == "__main__":
    main()