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)