print((function (_)
	local s,t,sa,sb,ta,tb=io.stdin:read("*l"),io.stdin:read("*l"),0,0,0,0
	for i=1,#s do if s:sub(i,i)=="A" then sa=sa+1 end end sb=#s-sa
	for i=1,#t do if t:sub(i,i)=="A" then ta=ta+1 end end tb=#t-ta
	return (sa>ta and ta or sa) + (sb>tb and tb or sb)
end)(io.stdin:read("*l")))