n=int(input())
s=[]
t=[]

def f():
	if len(t)==n:
		if all(t.count(c)>0 for c in "ABC"):
			s.append("".join(t))
	else:
		for c in "ABC":
			t.append(c)
			f()
	if len(t)>0:
		t.pop()
	return

f()

m=int(input())-1
if m<len(s):
	print(s[m])
else:
	print(-1)