# uses letter1 and letter2 as the combo letters
# returns length of longest alternating str with them, 0 if not possible
def getcombolength(s, letter1, letter2):
    count = 0
    toggleletter = '?'
    for letter in s:
        if letter == letter1 or letter == letter2:
            if letter == toggleletter:
                return 0
            count += 1
            toggleletter = letter
    return count

def alternate(s):
    if len(s) <= 1:
        return 0
    letters = 'abcdefghijklmnopqrstuvwxyz'
    maxcombo = 0
    for (letter1, letter2) in [(letters[j], letters[k]) for j in range(26) for k in range(j+1, 26)]:
        combo = getcombolength(s, letter1, letter2)
        maxcombo = max(combo, maxcombo)
    return maxcombo