from itertools import product
N = int(input())
S = int(input())
A = []
for a in product(["A","B","C"],repeat=N):
    if "A" in a and "B" in a and "C" in a:
        A.append("".join(a))
A = sorted(A)
if S>len(A):
    print(-1)
else:
    print("".join(A[S-1]))