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(arg) {
    var S = arg.split("");
    var cnt = 0;
    var skip = [];
    var firstFlg = true;
    
    for(var i = 0 ; i < S.length; i++) {
        if(S[i] == "W") {
            continue;
        }
        for(var j = 1 ; j < S.length-i ;j++) {
            if( S[i+j] == "B" || skip.indexOf(i) != -1) {
                continue;
            }
            
            if( S[i+j] == "W" ) {
                cnt++;
                if (firstFlg) {
                    skip.push(i+j);
                }
            }
        }
        firstFlg = false;
    }
    
    console.log(cnt);
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));