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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

main = do
  s <- getLine
  let ans = compute s
  print ans

{-
結局、左にBがある数だけ、Wを移動させることができる。
なので、前からなめて行って、Wが現れるたびに、それ以前に見たBの数を結果に加える。
でよいはず。
-}

compute :: String -> Int
compute s = loop 0 0 s
  where
    loop a _ "" = a
    loop a c ('B':s) = loop a (succ c) s
    loop a c ('W':s) = loop (a+c) c s