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: Runtime Error)

#include <iostream>
using namespace std;
int main(void){
    char tmp,s[100000];
    int cnt=0,j=0,k;
    bool check=false;
    cin>>s;
    
    while(s[j])
        j++;
        
        for(k=0;k<j;k++){
            if(s[k]=='B'&&s[k+1]=='W'){
            check=true;
            break;
            }
            check=false;
        }
    while(check==true){

        
        for(k=0;k<j;k++){
            if(s[k]=='B'&&s[k+1]=='W'){
            check=true;
            break;
            }
            check=false;
        }
        tmp=s[k];
        s[k]=s[k+1];
        s[k+1]=tmp;
        cnt++;
    }
    cout<<cnt-1;
}