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 PHP (5.6.30) (judge verdict: Time Limit Exceeded)

<?php
//error_reporting(0);
$N = trim(fgets(STDIN));
//list($N,$K) = explode(" ",trim(fgets(STDIN)));
//$a = explode(" ",trim(fgets(STDIN)));
//$H = explode(" ",trim(fgets(STDIN)));

$total = 0;
while(1) {
  $c = substr_count($N,"BW");
  if ($c==0) break;
  $total += $c;
  $N = str_replace("BW","WB",$N);
}
printf("%d\n",$total);