#yuki1724
n,k=map(int,input().split())
a=list(map(int,input().split()))
b=list(map(int,input().split()))
l=[]
for i in range(n):
 l.append((a[i]-b[i],i))
l.sort()
res=['A']*n
for i in range(n-k):
 res[l[i][1]]='B'
print(''.join(res))