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)

str = gets.chomp
maxCount = str.length - 1
count = 0
changeCount = 0
changeFlag = false

loop do 
  if str[count] == "B" && str[count+1] == "W"
    str[count] = "W"
    str[count+1] = "B"
    changeCount += 1
    changeFlag = true
  end
  count += 1
  if(count >= maxCount && changeFlag == false)
    break
  elsif(count >= maxCount)
    count = 0
    changeFlag = false
  end
end
puts changeCount