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 Python (3.4.3) (judge verdict: Wrong Answer)

from sys import stdin

def main():
    bw=stdin.readline().replace('B', '0').replace('W', '1')
    #A = list(map(int,stdin.readline().replace('B', '0').replace('W', '1')))

    A=[0,0,1]
    wc = A.count(1)
    indices = [i for i, x in enumerate(A) if x == 1]
    if wc > 0:
      print(sum(indices) - 1*wc*(wc-1) //2 )
    else:
      print(sum(indices))

input = lambda: stdin.readline()
main()