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.*;
import java.io.*;

class Main {
  int N, ans;
  char[] s;
  public static void main(String[] args) {
    Main m = new Main();
    m.input();
    m.solve();
    m.out();
  }

  public void input() {
    Scanner sc = new Scanner(System.in);
    s = sc.nextLine().toCharArray();
    sc.close();
  }

  public void solve() {
    N = s.length;
    int count = 0;
    ans = 0;
    for (int i = N-1; i >= 0; i--) {
      char target = s[i];
      if (target == 'W') {
        count++;
      } else if (target == 'B') {
        ans += count;
      }
    }
  }

  public void out() {
    System.out.println(ans);
  }
}