练习二

string=input("please input:")
str_list = list(string)
len_list = len(str_list)
middel = []
result = []
index = 0
for i in str_list:
    if index <= len_list-2:
        middel.append(i)
        for ind in range(index+1,len_list):
            if str_list[ind] in middel:
                break
            middel.append(str_list[ind])
        ls = ‘‘.join(middel)
        result.append(ls)
        middel=[]
    index = index+1
middel=[]
for ele in result:
    middel.append(len(ele))
index=middel.index(max(middel))
print(result[index])