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 irreversible_operation
  implicit none
  character(len=200000) :: s
  integer               :: i, j, n
  integer(8)            :: a, b
  read(*,*) s
  n = len_trim(s)
  a = 0
  b = 0
  j = 0
  do i = 1, n
     if (s(i:i) .eq. 'B') then
        a = a + n - j
        b = b + i
        j = j + 1
     end if
  end do
  write(*,'(i0)') a - b
  stop
end program irreversible_operation