n, k = map(int,input().split())
a = list(map(int,input().split()))
b = list(map(int,input().split()))

#まず全部Aを買うとすると、嬉しさはsum(a)
#Bに変えると差し引きB - A、これの大きい順にソートして貪欲


answer = ['A'] * n
c = []
for i in range(n):
    c.append((b[i] - a[i], i))
c.sort(reverse = True)

for i in range(n - k):
    answer[c[i][1]] = 'B'
print(''.join(answer))