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
   integer(8) ::i,j,k,le
   character*200000 s
   integer(8) ::counter=0,acount=0,dummy
!   integer,allocatable,dimension(:)::
   read(*,*)s
   le=len_trim(s)
   do i=1,le
      if(s(i:i)=="B")then
         acount=acount+i
      else
         counter=counter+1
      endif
   enddo
   write(*,*)(le-counter)*(le+counter+1)/2-acount
end program main