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

def BIT(bit, n):
    return bit//3**n%3
def code(s):
    return ord(s)-ord("A")
def codeR(n):
    return chr(ord("A")+n)

A = []
for bit in range(3**N):
    SET = set()
    for i in range(N):
        SET.add(BIT(bit, i))
    if len(SET) == 3:
        B = []
        for i in range(N):
            B.append(codeR(BIT(bit, i)))
        A.append("".join(B))

print(sorted(A)[S-1] if S <= len(A) else -1)