N, K = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

ans = ["B"] * N
D = [(A[i] - B[i], i) for i in range(N)]
D.sort(reverse=True)
for i in range(K):
    ans[D[i][1]] = "A"
print("".join(ans))