PTA乙级1029 python

s=input()
s1=input()
s2=[i for i in s1]
a=[]
i1=0
for i in s:
    if i !=s2[i1] and i.upper() not in a:
        a.append(i.upper())
    elif i==s2[i1] and i1!=len(s2)-1:
        i1+=1
print(''.join(a))