第三章 7-17 输出10个不重复的英文字母

s=input()
new=[]
for i in s:
    if i.isalpha():
        if not i in new and not i.upper() in new and not i.lower() in new:
            new.append(i)
if len(new)>=10:
    print(''.join(new[:10]))
else:
    print('not found')