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;
using System.Text.RegularExpressions;

class Amondai
{
    static void Main()
    {
        var str=Console.ReadLine();
        var ans = 0L;
        var s = "BW";
        Regex match = new Regex("BW");
        while (str.Contains(s))
        {
            ans += StrCount(str);
            str = str.Replace("BW","WB");
        }
        Console.WriteLine(ans);
    }

    static long StrCount(string str)
    {
        var index = 0;
        var count = 0L;
        var length = str.Count();
        while (index<length-1) {
            index = str.IndexOf("BW", index);
            if (index == -1) break;
            index++;
            count++;
        }
        return count;
    }
}