func main()
	var ss: [][]char :: cui@input().split(" ")
	var n: int :: ss[0].toInt(&)
	var m: int :: ss[1].toInt(&)
	var s: []char :: cui@input()
	var t: []char :: cui@input()
	
	var sa: int :: 0
	for i(0, n - 1)
		if(s[i] = 'A')
			do sa :+ 1
		end if
	end for
	var ta: int :: 0
	for i(0, m - 1)
		if(t[i] = 'A')
			do ta :+ 1
		end if
	end for
	var ans: int :: [sa, ta].min() + [n - sa, m - ta].min()
	do cui@print("\{ans}\n")
end func