import sys

lines = sys.stdin.read().split('\n')

for i in range(len(lines) // 2):
	count = int(lines[i*2])
	items = [int(x) for x in lines[i*2+1].split(' ')]
	items.reverse()

	if len(items) > 1:
		d = items[1] - items[0]

		for i, value in enumerate(items):
			if i > 1 and items[i] - items[i - 1] != d:
				print(len(items) - i + 1)
				break
		else:
			print('1')
	else:
		print('1')