from itertools import product

n = int(input())
s = int(input())

result = set()
for a in product(["A", "B", "C"], repeat=n):
    if "A" in a and "B" in a and "C" in a:
        result.add(a)

ans = list(result)
ans.sort()

print("".join(ans[s-1]) if len(ans) >= s else -1)