import math

n = int(input())
perfs = [int(input()) for _ in range(n)]

if n == 0:
    print(0)
else:
    # Calculate sum_denominator and sum_81
    sum_denominator = 9.0 * (1.0 - (0.9 ** n))
    sum_81 = 0.81 * (1.0 - (0.81 ** n)) / 0.19
    sqrt_sum_81 = math.sqrt(sum_81)
    F_n = sqrt_sum_81 / sum_denominator

    # Calculate F_inf
    F_inf = math.sqrt(0.81 / 0.19) / 9.0  # Precomputed value for F(∞)
    F1 = 1.0  # F(1) is always 1.0
    numerator_f = F_n - F_inf
    denominator_f = F1 - F_inf
    f_n = (numerator_f / denominator_f) * 1200.0

    # Calculate sum_g
    sum_g = 0.0
    for i in range(n):
        exponent = i + 1
        weight = 0.9 ** exponent
        perf = perfs[i]
        g_val = 2.0 ** (perf / 800.0)
        sum_g += g_val * weight

    avg_g = sum_g / sum_denominator
    g_inv = 800.0 * math.log2(avg_g)
    rating = g_inv - f_n

    # Rounding to the nearest integer, considering the allowed error
    print(round(rating))