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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<cmath>
#include<map>
#include<stack>
#include<queue>
#include<bitset>

#define ipair pair<int,int>
#define rep(i,n) for(i=0;i<n;i++)

using namespace std;

typedef long long int lli;
typedef vector<int> vi;

int main() {
	string s;
	lli i, j, k, n, l, m, bc, wc;

	cin >> s;

	k = s.length();
	
	m = 0;
	j = 0;
	rep(i, k) {
		if (s[i] == 'W') {
			m += i - j;
			j++;
		}
	}

	cout << m;

	return 0;
}