N,K = map(int,input().split())
A = list(map(int,input().split()))
B = list(map(int,input().split()))
C = [(a-b,i) for i,(a,b) in enumerate(zip(A,B))]
C.sort()
flg = ["B"]*N
for i in range(K):
    d,k = C[-1-i]
    flg[k] = 'A'
print(''.join(flg))