最长不重复字符串

import sys 
a=sys.stdin.readline().strip()
length=0
i=0
while i <len(a):
    l = 0
    j=i+1
    while j<len(a)+1:
        b=a[i:j].count(a[j-1])
        if b==1:
            l+=1
        else:
            break
        j+=1
    if l>length:
        length=l
    if j<len(a):
        i = j
    else:
        break
sys.stdout.write(str(length))