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 PyPy3 (2.4.0) (judge verdict: Time Limit Exceeded)

B = input()
Bin = []
lb = len(B)
Bin.append(2)
for i in range(lb):
    if B[i] == "W":
        Bin.append(0)
    else:
        Bin.append(1)
num = 0
i = 0
while i < lb:
    if Bin[i] == 1 and Bin[i+1] == 0:
        Bin[i] = 0
        Bin[i+1] = 1
        num = num + 1
        i = i - 1
    else:
        i = i + 1
print(num)