题解 | 好串

# 好串的条件，与a最近的b必须在a的后面，ab数量相等
def main():
    s = input()
    stack = []
    for char in s:
        if char == "a":
            stack.append(char)
        elif char == "b":
            if not stack:
                print("Bad")
                return
            stack.pop()
        else:
            print("Bad")
            return

    if not stack:
        print("Good")
    else:
        print("Bad")
main()