18

with open('24.txt') as f:
    a = f.readline()
    a = list(map(lambda a: a[1], sorted(list(filter(lambda x: x[0] == 'A', zip(a, a[1:]))))))


def f(a, b):
    if a == b:
        return a
    if a != b:
        return a + ' '


symb = list(map(f, a, a[1:]))
symb = (''.join(symb) + a[-1]).split()
symlen = list(map(len, symb))
print(symb[symlen.index(max(symlen))][0])