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 Lua (5.3.2) (judge verdict: Wrong Answer)

S = {}

for w in string.gmatch(io.read(), "%a") do
  table.insert(S,w)
end

C = 0
mc = 0
bf = 0

for i=2, #S do
  p = table.concat(S,"",i-1,i);
  if p == "BW" then
    mc = mc + 1
    C = C + bf
    bf = 0
    i = i + 1
  else
    mc = 0
    if p == "BB" then
      bf = 1
    else
      bf = 0
    end
  end

  C = C + mc
end

print(C)