while 1:

	k = int(input())

	if not k: break

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

	k = eval(input())

	if not k: break

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

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

-    k = int(input()) +    k = eval(input())