from math import log2

N=int(input())
P=[int(input()) for i in range(N)]

def F(n):
    x=0
    y=0

    for i in range(1,n+1):
        x+=0.81**i
        y+=0.9**i

    return (x**(1/2))/y


#for i in range(1,1000):
#    print(F(i))

F_inf=0.22941573387056197

def f(n):
    return (F(n)-F_inf)/(F(1)-F_inf)*1200

def g(x):
    return 2**(x/800)

def g_inv(x):
    return 800*log2(x)

x=0
y=0
for i in range(1,N+1):
    x+=g(P[i-1])*(0.9**i)
    y+=0.9**i

print(g_inv(x/y)-f(N))