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 Ruby (2.3.3) (judge verdict: Time Limit Exceeded)

s = gets.chomp.split("")
ans = 0

0.upto(s.length - 2) do |i|
  if s[i] == "B" && s[i + 1] == "W"
    s[i] = "W"
    s[i + 1] = "B"
    ans += 1

    i.downto(1) do |j|
      if s[j] == "W" && s[j - 1] == "B"
        s[j] = "B"
        s[j - 1] = "W"
        ans += 1
      else
        break
      end
    end
  end
end

puts ans