import sys


def main():
    input = lambda: sys.stdin.readline()[:-1]
    N = int(input())
    A = list(map(int, input().split()))

    n = 1000
    for ai in A:
        n *= (1000 - ai) / 1000
    print(1000 - n)


if not __debug__:
    f = open(sys.argv[1], "r")
    sys.stdin = f

main()