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 Scala (2.11.7) (judge verdict: Wrong Answer)

object Main extends App {
  private def func(s:Array[Char]):Int = {
    var count = 0
    var last = 0
    //do{
      var i=0
      while(i < s.size){
        if(s(i)=='W'){
          last += 1
          count += (i - last + 1)
        }
        i+=1
        //println(count, i, find, s.toSeq)
      } 
    //} while(false/*find*/)
    count
  }
  println(func(io.Source.stdin.getLines.toIndexedSeq.head.toCharArray))
}