n=int(input())
s=int(input())
a=[]
for i in range(3**n):
	b=[]
	A=False
	B=False
	C=False
	for j in range(n):
		x=i//pow(3,j)%3
		if x==0:
			b.append('A')
			A=True
		elif x==1:
			b.append('B')
			B=True
		else:
			b.append('C')
			C=True
	if A and B and C:
	    a.append(''.join(b))
a.sort()
if s<=len(a):
    print(a[s-1])
else:
    print(-1)