题解 | #计算字符串的距离#

while True:
    try:
        the_str = input()
        char_map = {}
        for i in range(len(the_str)):
            if the_str[i] not in char_map.keys():
                char_map[the_str[i]] = True
            else:
                char_map[the_str[i]] = False
        exist = False
        for key, value in char_map.items():
            if value == True:
                print(key)
                exist = True
                break
        if exist == False:
            print(-1)
    except:
        break