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 C (GCC 9.2.1) (judge verdict: Time Limit Exceeded)

#include <stdio.h>
#include <string.h>

char S[222222];

int main(void) {
	int i, l;
	int kugyu = 0;
	if (scanf("%222221s", S) != 1) return 1;
	l = (int)strlen(S);
	for (;;) {
		int kitaeri = kugyu;
		for (i = l - 2; i >= 0; i--) {
			if (S[i] == 'B' && S[i + 1] == 'W') {
				S[i] = 'W';
				S[i + 1] = 'B';
				kugyu++;
			}
		}
		for (i = 0; i + 1 < l; i++) {
			if (S[i] == 'B' && S[i + 1] == 'W') {
				S[i] = 'W';
				S[i + 1] = 'B';
				kugyu++;
			}
		}
		if (kitaeri == kugyu) break;
	}
	printf("%d\n", kugyu);
	return 0;
}