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;

namespace A
{
	class Program
	{
		static void Main(string[] args)
		{
			var S = Console.ReadLine().ToCharArray();

			int count = 0;
			while(true) {
				int swap = -1;
				for(int i=0; i<S.Length-1; i++)
					if(S[i] == 'B' && S[i+1] == 'W') {
						swap = i;
						break;
					}
				if(swap == -1) break;
				S[swap] = 'W';
				S[swap+1] = 'B';
				count++;
			}
			Console.WriteLine(count);
		}
	}
}