func main()
	var s: []char :: cui@input()
	var ans: int :: 0
	var cnt: int :: 0
	for i(0, ^s - 1)
		if(s[i] = 'B')
			do cnt :+ 1
		else
			do ans :+ cnt
		end if
	end for
	do cui@print("\{ans}\n")
end func