import sys

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

count = int(lines[0])
items = [int(x) for x in lines[1].split(' ')]
items.reverse()

print(items)

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)
			sys.exit(0)

print('1')
sys.exit(0)