题解 | 好串

def get_id(c):
    if c == "a":
        return 1
    if c == "b":
        return 2
    return 0

def main():
    string = input()
    s = []
    flag = True

    for c in string:
        id = get_id(c)
        if id == 2:
            if not s or id + s[-1] != 3:
                flag = False
                break
            else:
                s.pop()
        if id == 1:
            s.append(id)

    if flag and not s:
        print("Good")
    else:
        print("Bad")

if __name__ == "__main__":
    main()