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: Wrong Answer)

function main(arg) {
	var src = arg.split("\n")[0].split("")
	var register = []
	var sum_counter = 0
	for (var n = 0; n < 100;n++) {
		var counter = 0
		for (var i = 0; i < src.length; i++) {
			if (src[i] === "B" && src[i+1] === "W") {
				src[i] = "W"
				src[i + 1] = "B"
				var key = String(i) + ":" + String(i + 1)
				// if (register.includes(key)) {
				// 	continue
				// }
				register.push(key)
				counter++
				i++
				// console.log(key)
			}
		}
		// console.log(src)
		// console.log("")
		sum_counter += counter
		if (counter === 0) {
			break
		}
	}
	console.log(sum_counter)
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));