前三个错了：

Wrong Answer.wrong answer Too short on line 1.

a=str(input())
c=1
for i in range(len(a)):
    if(a.count(a[i])==1):#找a[i]在a中的出现次数
        c=0
        b=a[i]
        break
if(c==0):
    print(b)
else:
    print('no')