题解 | #找出字符串中第一个只出现一次的字符#

while True:
    try:
        s = input()
        dic = {} #字典
        for i in s:
            dic[i] = dic.get(i, 0)+1 #遍历更新值
        if sum(dic.values())/len(dic) >= 2: #若无只出现一次的字符，打印-1
            print(-1)
        else: 
            for k in dic.keys():
                if dic[k]==1:
                    print(k) #若有，打印字符
                    break
    except:
        break