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: Wrong Answer)

import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Main {
	
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String input = sc.nextLine();
		sc.close();
		List<String> stringArr = Arrays.asList(input.split(""));
		
		int ans = 0;
		
		int wCnt = 0;
		for(int i = stringArr.size() - 1; i >= 0; i--) {
			if(stringArr.get(i).contentEquals("B")) {
				ans+= wCnt;
			}else {
				wCnt++;
			}
		}
		
		System.out.println(ans);
	}
	
//	public static void swap(int a, int b,List<String> strArr) {
//		String aElm = strArr.get(a);
//		String bElm = strArr.get(b);
//		strArr.set(b, aElm);
//		strArr.set(a, bElm);
//	}
}