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

ave=sum(x)/n
xx=[(i-ave)**2 for i in x]
hyojunhensa=(sum(xx)/n)**0.5

if hyojunhensa==0:
    print(50)
else:
    print(int((x[m-1]-ave)*10/hyojunhensa+50))