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

now = 0
for i in range(3**N):
    a = []
    for j in range(N-1,-1,-1):
        v = (i//(3**j))%3
        if(v == 0):
            a.append("A")
        elif(v == 1):
            a.append("B")
        else:
            a.append("C")
    if(len(set(a)) == 3):
        now += 1
        if(now == S):
            print("".join(a))
            exit()
print(-1)