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