N,D=map(int,input().split())

B=[[]]
for i in range(N):
    TMP=[]
    for b in B:
        for j in (0,1,2):
            TMP.append(b+[j])
    B=TMP

S=[]
R=['C','A','B']

for b in B:
    if sum(b)==D:
        x=''
        for i in b:
            x+=R[i]
        S.append(x)

print(min(S))