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: Wrong Answer)

s = gets.chomp

cnt = 0

while true
  if s =~ /\ABW/
    first, latter = s.split(/\ABW+/)
  elsif s =~ /BW+\z/
    first, _latter = s.split(/BW+\z/)
    latter = ''
  else
    first, latter = s.split(/BW+/)
  end

  break unless latter
  first_length = first.length
  latter_length = latter.length
  w_length = s.length - first_length - latter_length - 1
  cnt += w_length
  s = "#{first}#{'W' * w_length}B#{latter}"
end

puts cnt