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 Go (1.6) (judge verdict: Time Limit Exceeded)

package main

import (
	"fmt"
)

func main() {

	var S string

	fmt.Scan(&S)

	status :=  make(map[int]string)

	for i:=0;i<len(S);i++{

		status[i] = S[i:i+1]
	}

	tmpcnt :=0
	cnt := 0

	for{

		tmpcnt=0

		for i:=0;i<len(S)-1;i++{

			if status[i] == "B" && status[i+1]=="W"{

				status[i]="W"
				status[i+1] = "B"
			
				tmpcnt++
			}
		}

		cnt += tmpcnt

		if tmpcnt < 1{

			break
		}

	}

	fmt.Println(cnt)

}