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

s = input("insert some string: ")
start = 0
end = 0
temp = ""
while end+1 = s[end]:
        end += 1
    if len(s[start:end+1]) > len(temp):
        temp = s[start:end+1]
    end +=1
    start = end
print("longest ordered part is: "+temp)