题解 | #找出字符串中第一个只出现一次的字符#

s = input()
dic = {}

for i in s:
   if i not in dic:
      dic[i] = dic.get(i,0) + s.count(i)
      if dic[i] == 1:
         print(i)
         break
if min(dic.values()) > 1:
    print(-1)