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 5.4.1) (judge verdict: Runtime Error)

#include <stdio.h>

char s[100];
int c = 0;

void r(int i) {
	for (; i > 0; i--) {
		if (s[i] == 'W' && s[i - 1] == 'B') {
			s[i] = 'B';
			s[i - 1] = 'W';
			c++;
			r(i - 1);
		}
	}
}

int main (void) {
	gets(s);
	int l;
	for(l = 0; s[l] != 0; l++);
	r(l - 1);
	printf("%d\n", c);
	return 0;
}