N, K = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
L = []
for j in range(N):
  L.append((A[j] - B[j], j))
L.sort(reverse=True)
ans = ['B'] * N
for j in range(K):
  ans[L[j][1]] = 'A'
print(''.join(ans))