n, d = map(int, input().split())
s = []
for i in range(1, n+1)[::-1]: 
    if d == 0:
        s.append('C')
    elif d/i == 2:
        d -= 2
        s.append('B')
    else:
        d -= 1
        s.append('A')
print(''.join(s))