N, K = map(int, input().split())
A = map(int, input().split())
B = map(int, input().split())
D = [(b - a, i) for i, (a, b) in enumerate(zip(A, B))]
D.sort()

ans = ['B'] * N
for x, i in D[:K]:
    ans[i] = 'A'
print(''.join(map(str, ans)))