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.io.*;
import java.util.StringTokenizer;

public class Main {


  private void solve(InputReader in, PrintWriter out) {
    String s = in.next();
    char[] chars = s.toCharArray();
    int w = 0;
    int b = 0;
    for (int i = 0; i < chars.length; i++) {
      if (chars[i] == 'B') {
        b++;
      } else {
        w++;
      }
    }
    out.print(Math.min(w, b) * 2);

  }


  public static void main(String[] args) {
    new Main().run();
  }

  private void run() {

    try (InputReader in = new InputReader(System.in);
         PrintWriter out = new PrintWriter(System.out)) {
      solve(in, out);
    }
  }


  static class InputReader implements AutoCloseable {
    private BufferedReader reader;
    private StringTokenizer tokenizer;

    InputReader(InputStream stream) {
      //reader = new BufferedReader(new FileReader(stream), 32768);
      reader = new BufferedReader(new InputStreamReader(stream), 32768);
      tokenizer = null;
    }

    String next() {
      while (tokenizer == null || !tokenizer.hasMoreTokens()) {
        try {
          tokenizer = new StringTokenizer(reader.readLine());
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
      }
      return tokenizer.nextToken();
    }

    public int nextInt() {
      return Integer.parseInt(next());
    }

    public long nextLong() {
      return Long.parseLong(next());
    }

    public double nextDouble() {
      return Double.parseDouble(next());
    }

    @Override
    public void close() {
    }
  }

}