#The solution in Python 3 is as follows:
while True:
n = int(input())
if n == -1: break
A = [int(input()) for _ in range(n)]
s = sum(A)
if s%n: #check if the candies can be distributed equally
print(-1)
else:
print(sum(abs(s//n-a) for a in A)//2)
#Keep visiting for more solutions of SPOJ problems in Python 3.Thank you!!!
