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

ave=sum(x)/n
xx=[]
for i in x:
    xx.append((i-ave)**2)
bunsan=sum(xx)/n
hyojunhensa=bunsan**0.5
hensachi=[]
if hyojunhensa==0:
    print(50)
else:
    for i in x:
        tmp=abs(i-ave)*10
        tmp/=hyojunhensa
        if (i-ave)<0:
            tmp*=-1
        hensachi.append(50+tmp)
    print(int(hensachi[m-1]))