n,k=map(int,input().split())
a=list(map(int,input().split()))
b=list(map(int,input().split()))
lis=[]
for i in range(n):
	lis.append((a[i]-b[i],i))
lis.sort()
ans=["A"]*n
for i in range(n-k):
	ans[lis[i][1]]="B"

print("".join(ans))