import sys
from typing import List, Tuple

sys.setrecursionlimit(10 ** 6)

MOD = 998244353

int1 = lambda x: int(x) - 1
input = lambda: sys.stdin.readline().rstrip('\n')
ii = lambda: int(input())
vi = lambda: list(map(int, input().split()))
vi1 = lambda: list(map(int1, input().split()))


def dbg(*args, **kwargs):
    print(*(repr(arg) for arg in args), *(f'{k}: {repr(v)}' for k, v in kwargs.items()),
          sep='; ', file=sys.stderr, flush=True)


def main():
    n = ii()
    s = int1(input())

    a = ['']
    for i in range(n):
        b = []
        for i in a:
            b.append(i + 'A')
            b.append(i + 'B')
            b.append(i + 'C')
        a = b
    a = [x for x in a if 'A' in x and 'B' in x and 'C' in x]

    if s < len(a):
        return a[s]
    return -1


def _start():
    if (ret := main()) is not None:
        print(*ret) if isinstance(ret, List) or isinstance(ret, Tuple) else print(ret)


if __name__ == '__main__':
    _start()