def seq(n):
  arr = []

  arr = [int(i) for i in input().split(' ')]


  if len(arr) == 1:
    return 1

  diff = arr[-1] - arr[-2]
  index = n - 1
  
  for i in range(1, n):
    d = arr[n - i - 1] - arr[n -i - 2]
    if d != diff:
      return n - i

  return 1

n = 0

while n is not None:
  if int(n) > 0:
    print(seq(int(n)))
  n = input()