n, d = map(int, input().split())
YZX = []
for z in reversed(range(n+1)):
    x = n-d+z
    y = d-2*z
    if x >= 0 and y >= 0:
        #s = 'A'*y+'B'*z+'C'*x
        YZX.append((y, z, x))
YZX.sort(key=lambda x: (-x[0], -x[1], -x[2]))
y, z, x = YZX[0]
s = 'A'*y+'B'*z+'C'*x
print(s)