from itertools import product

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

X = ['A', 'B', 'C']
cnt = 0
for v in product(X, repeat=N):
  if 'A' in v and 'B' in v and 'C' in v:
    cnt += 1
  if cnt == S:
    print(''.join(v))
    exit()

print(-1)