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 C# (Mono 4.6.2.0) (judge verdict: Time Limit Exceeded)

using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
  static void Main(string[] args)
  {
    var c = Console.ReadLine().ToCharArray();
    int count = 0;
    Change(ref c, ref count);
    
    Console.WriteLine(count);
  }
  
  static void Change(ref char[] c, ref int count){
    bool isChange = false;
    for(int i=0; i<c.Length-1; i++){
      if(c[i]=='B' && c[i+1]=='W'){
        isChange = true;
        c[i]='W';
        c[i+1]='B';
        count++;
      }
    }
    if(isChange){
      Change(ref c,ref count);
    }
  }
}