遞迴下降剖析器Recursive-descent parser

try:
	while True:
		yue = input()
		yue = yue.replace('\r', '')
		S = 'S'

		for x in range(len(yue)):
			if (yue[x] == '+'):
				S = S.replace('S', '+SS', 1)
			elif yue[x] == "-":
				S = S.replace('S', '-SS', 1)
			else:
				S = S.replace('S', 'a', 1)

		if S == yue:
			print("accept")
		else:
			print("error")
except EOFError:
	pass