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 JavaScript (node.js v5.12) (judge verdict: Time Limit Exceeded)

function main(input){
    lines = input;

    var count=0;
    var flg=true;
    var flgsub=true;
    while(flg){
        flg=false;
        flgsub=true;
        for(var i=0;i<lines.length-1;i++){
            var a=lines.charAt(i);
            var b=lines.charAt(i+1);

            if(a=="B" && b=="W"){
                lines=lines.slice(0,i) +"WB"+ lines.slice(i+2);
                count++;
                flg=true;
                flgsub=false;
            }else if(flgsub){
                if(a=="W"){
                    lines=lines.slice(1);
                    i--;
                }
            }
        }
    }

    console.log(count);
}

main(require('fs').readFileSync('/dev/stdin','utf8'));