import math

n = int(input())
A = list(map(int, input().split()))
m = int(input())

ave = sum(A) / n

q1 = [((a - ave) ** 2) for a in A]
if sum(q1) == 0:
    print(50)
    exit()
q2 = math.sqrt(sum(q1) / n)
q3 = abs(A[m - 1] - ave) * 10 / q2
if A[m - 1] > ave:
    print(int(50 + q3))
else:
    print(int(50 - q3))