N,K = map(int,input().split())
A = list(map(int,input().split()))
B = list(map(int,input().split()))
C = sorted([(i,A[i]-B[i]) for i in range(N)],key=lambda x:-x[1])
S = [0]*N
ans = 0
for i in range(N):
    if i<K:
        S[C[i][0]] = "A"
    else:
        S[C[i][0]] = "B"
print("".join(S))