Problem:
Score : 300 points

Problem Statement

There are N Reversi pieces arranged in a row. (A Reversi piece is a disc with a black side and a white side.)
The state of each piece is represented by a string S of length N.
If S_i=B, the i-th piece from the left is showing black;
If S_i=W, the i-th piece from the left is showing white.

Consider performing the following operation:

Choose i (1 \leq i < N) such that the i-th piece from the left is showing black and the (i+1)-th piece from the left is showing white, then flip both of those pieces. That is, the i-th piece from the left is now showing white and the (i+1)-th piece from the left is now showing black.

Find the maximum possible number of times this operation can be performed.

Constraints

1 \leq |S| \leq 2\times 10^5

S_i=B or W

Input

Input is given from Standard Input in the following format:

S

Output

Print the maximum possible number of times the operation can be performed.

Sample Input 1

BBW

Sample Output 1

2

The operation can be performed twice, as follows:

Flip the second and third pieces from the left.

Flip the first and second pieces from the left.

Sample Input 2

BWBWBW

Sample Output 2

6

Solution in Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program main
implicit None
character*200000::s
integer(8)::k,t,i,n
integer(8),allocatable::a(:)

read *,s
k = len_trim(s)
t = 0

do i = k,1,-1
	if(s(i:i) == "B")then
	t = t + 1
	endif
enddo

if(t == 0)then
	print 101,t
	stop
endif

allocate(a(t))

n = 1
do i = k,1,-1
	if(s(i:i) == "B")then
		a(n) = i
		n = n + 1
	endif
enddo

n = 0
do i = 1,t
	n  = n + k - (a(i)) -(i -1)
enddo

print 101,n
deallocate(a)

101 format(i0)
end program main