N=int(input())
S=int(input())
a=[]
for i in range(3**N):
    l=[]
    for j in range(N):
        if (i//(3**j))%3==0:
            l.append("A")
        elif (i//(3**j))%3==1:
            l.append("B")
        else:
            l.append("C")
    if ("A" not in l) or ("B" not in l) or ("C" not in l):
        continue
    a.append("".join(l))
a.sort()
if len(a) < S:
    print(-1)
else:
    print(a[S-1])