s = 'abcxauefghvxuvw'

# s = xxxxxxxxxxxxxDEFGHAxxxxxxxxxxxxxxxx
#                  i    j

i = 0

longest = ''

while i < len(s):
    j = i + 1
    while j < len(s) and ord(s[j]) == ord(s[j - 1]) + 1:
        j += 1
    # print(s[i:j])

    if j - i > len(longest):
        longest = s[i:j]

    i = j

print('den længste blok af stigende tegn er', longest)