from itertools import product

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

res=[]
def change(num):
    if num == 1:
        return "A"
    elif num == 2:
        return "B"
    else:
        return "C"
for i in product(*(range(1, 4) for i in range(N))):
    ele = ""
    for j in range(N):
        ele += change(i[j])
    if "A" in ele and "B" in ele and "C" in ele:
        res.append(ele)

res=sorted(res)
try:
    print(res[S-1])
except:
    print(-1)