while 1:

  k = eval(input()) - 1

  if not k+1: break

  print(sum(map(int,input().split()))/k)
while 1:

  k=eval(input())

  if not k:break

  print(sum(map(int, input().split()))/(k-1))
while 1:
    k = eval(input()) - 1
    if not k + 1:
        break
    print(sum(map(int, input().split())) / k)

while 1:
    k = eval(input())
    if not k:
        break
    print(sum(map(int, input().split())) / (k - 1))

-    k = eval(input()) - 1 -    if not k + 1: +    k = eval(input()) +    if not k: -    print(sum(map(int, input().split())) / k) +    print(sum(map(int, input().split())) / (k - 1))