gets;
tops, bottoms = Hash.new(0), Hash.new(0)

gets.chomp.chars do |i|
	tops[i.to_s] += 1
end

gets.chomp.chars do |i|
	bottoms[i.to_s] += 1
end

print [tops["A"], bottoms["A"]].min + [tops["B"], bottoms["B"]].min