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

ave = sum(students) / n

std = (sum((student - ave) ** 2 for student in students) / n) ** 0.5

for i in range(m):
    if i == m - 1:
        print(int(((students[i] - ave) / std) * 10 + 50))
        break