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

xs = [(a - b, i) for i, (a, b) in enumerate(zip(A, B))]
xs.sort(reverse=True)

cs = ['B'] * N
for i in range(K):
    p = xs[i][1]
    cs[p] = 'A'

print(*cs, sep='')