import sys
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
INF = 2 ** 63 - 1
mod = 998244353

n = ii()

a = li()

speed = [0] * (n)

speed[0] = 1000

for i in range(n - 1):
    speed[i + 1] = speed[i] * (1000 - a[i]) / 1000

print(1000 - speed[n - 1])