n, d = map(int, input().split())

ans = 'D' * n
for i in range(d // 2 + 1):
    j = d - 2 * i
    k = n - i - j
    if k < 0:
        continue
    ans = min(ans, 'A' * j + 'B' * i + 'C' * k)
print(ans)