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.*;
public class Main {
	public static void main(String[] args) {
        // 文字をキーボードから入力し、配列に記憶
        // Scannerクラスのインスタンスの生成
        Scanner scan = new Scanner(System.in);
        String str = scan.next();
        
        int n = 0;
        int a = 0;
        int flag = 0;
        
        for (int i = 0; i < str.length(); i++) {
        	if(str.charAt(i) == 'B' && flag == 0) {
        		flag = 1;
        	}
        	if(flag == 1) {
        		if(str.charAt(i) == 'W') {
        			n += a;
        		}
        		if(str.charAt(i) == 'B') {
        			a++;
        		}
        	}
        }
        System.out.println(n);
	}
}