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 Java8 (OpenJDK 1.8.0) (judge verdict: Time Limit Exceeded)

import java.util.*;
import java.math.*;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		String str = sc.next();
		String[] strArray = str.split("");
		int[] intArray = new int[strArray.length];
		Map<Integer, Integer> numMap = new HashMap<>();
		int count = 0;
		boolean flag =true;
		int preCount = 0;

		for (int i = 0; i <strArray.length; i++) {
			// intArray[i]=strArray[i].equals("B")?1:0;
			int value = strArray[i].equals("B")?1:0;
			numMap.put(i,value);
			// System.out.println(intArray[i]);
		}

			for (int i = 0; i <numMap.size()-1; i++) {
				// System.out.print(intArray[i] + "+"+intArray[i+1]);
				// System.out.print(intArray[i]==1);
				// System.out.println(intArray[i+1]==0 );
				if(numMap.get(i)==1 && numMap.get(i+1)==0){
					numMap.put(i,0);
					numMap.put(i+1,1);
					count ++;
					i -=2;
					if(i==-2){
						i=0;
					} 
				}
			}
		System.out.println(count);




	}
}