24 (ABABABABAB)

s = open("24.txt").readline()
answ = 0
cur = 0 #текущая длина
a = 'AB'
for e in s:
    if e == a[cur % 2]:
        cur += 1
        answ = max(answ, cur)
    else:
        if e == 'A':
            cur = 1
        else:
            cur = 0
print(answ)