Finding longest substring in alphabetical order

Question

EDIT: I am aware that a question with similar task was already asked in SO but I\'m interested to find out the problem in this specific piece of code. I am

Answer 1

a lot more looping, but it gets the job done

s = raw_input("Enter string")
fin=""
s_pos =0
while s_pos < len(s):
    n=1
    lng=" "
    for c in s[s_pos:]:
        if c >= lng[n-1]:
            lng+=c
            n+=1
        else :
            break
    if len(lng) > len(fin):
        fin= lng`enter code here`
    s_pos+=1    
print "Longest string: " + fin