import sys
input = sys.stdin.readline

N = int(input())
A = list(map(int, input().split()))
speed = [0] * N
speed[0] = 1
for i in range(N-1):
    t = 1000/speed[i]
    speed[i+1] = speed[i] - A[i]/t
print(1000-speed[N-1]*1000)