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(reverse=True)
ans=['B']*n
for i in range(k):
    ans[l[i][1]]='A'
print(''.join(ans))