mod = 998244353


def main():
    import sys
    input = sys.stdin.readline

    N = int(input())
    A = list(map(int, input().split()))

    r = 1
    for a in A:
        r *= (1000 - a) / 1000
    print(1000 - 1000 * r)


if __name__ == '__main__':
    main()