N, K = gets.split(" ").map{|s| s.to_i}

a = gets.split(" ").map{|s| s.to_i}
b = gets.split(" ").map{|s| s.to_i}

d = a.zip(b).map.with_index{|x, i| [x[0]-x[1], i]}.sort.reverse

ans = ["B"]* N

d[0,K].each{|v, i|
	ans[i] = "A"
}

puts ans.join("")