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

C = [(B[i] - A[i], i )for i in range(N)]
C.sort()

ans = [''] * N
for i in range(N):
    _, num = C[i]
    if i < K:
        ans[num] = 'A'
    else:
        ans[num] = 'B'
print(''.join(ans))