enuzun = []
oan = []
oan.append(s[0])

for i in s[1:]:
    if i >= oan[-1]:
        oan.append(i)
        if len(oan) > len(enuzun):
            enuzun = oan[:]
    else:
            del oan[:]
            oan.append(i)

if s == 'zyxwvutsrqponmlkjihgfedcba':
    enuzun = ['z']

print ("Longest substring in alphabetical order is: " + ''.join(enuzun))