from itertools import product


def make(n: int):
    res = []
    for ps in product(range(3), repeat=n):
        if not all(x in ps for x in [0, 1, 2]):
            continue

        res.append(ps[:])

    return res


N = int(input())
S = int(input())

cands = make(N)
if S > len(cands):
    print(-1)
    exit()

d = {0: 'A', 1: 'B', 2: 'C'}
ans = ''.join(d[x] for x in cands[S-1])
print(ans)