题解 | #找出字符串中第一个只出现一次的字符#

s = input()
d = {}
for i in s:
    if i not in d:
        d[i] = s.count(i)
ls = []
for k,v in d.items():
    if v == 1:
        ls.append(k)
if len(ls) != 0:
    print(ls[0])
else:
    print(-1)