import math

N = int(input())
RPref = []
for i in range(N):
    RPref.append(input())

Fn_inf = 0.22941573387056197


def Fn(N):
    molecule = 0
    denominator = 0
    for i in range(N):
        molecule += math.pow(0.81, i)
        denominator += math.pow(0.9, i)
    return math.sqrt(molecule) / denominator
Fn


def fn(n):
    molecule = Fn(n) - Fn_inf
    denominator = Fn(1) - Fn_inf
    return (molecule / denominator) * 1200
fn


def gx(x):
    return math.pow(2.0, (x/800))
gx


def invgx(x):
    return 800 * math.log(x) / math.log(2.0)
invgx


def Rating(n):
    molecule = 0
    denominator = 0
    for i in range(n):
        molecule += gx(int(RPref[i]))*math.pow(0.9, i)
        denominator += math.pow(0.9, i)
    return (invgx(molecule / denominator) - fn(n))
Rating


print(Rating(N))