"""

https://yukicoder.me/problems/no/3135

2**12

"""

import sys

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

cnt = 0
for bit in range(3**N):

    A = []    

    for i in range(N):
        A.append( bit % 3 )
        bit //= 3

    if len(set(A)) == 3:
        cnt += 1

    if cnt == S:
        A.reverse()
        ans = [ "ABC"[x] for x in A ]
        print (*ans, sep="")
        sys.exit()

print (-1)