题解 | 好串

class Stack:
    def __init__(self) -> None:
        self.items = []
    def push(self,x):
        self.items.append(x)
    def pop(self):
        if not self.is_empty():
            self.items.pop()
    def is_empty(self):
        return len(self.items) == 0

a = str(input())
s = Stack()
for char in a:
    if char == "a":
        s.push(char)
    elif char == 'b':
        if not s.is_empty():
            s.pop()
        else:
            print("Bad")
            break
else:
    if s.is_empty() == True:
        print("Good")
    elif s.is_empty() == False:
        print("Bad")