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: Wrong Answer)

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

int get(char *s,int k,int l);

int main()
{
    int i,j,k=0,l;
    char s[200001],tmp;

    scanf("%s",s);

    l=strlen(s);
    k=get(s,k,l);

    printf("%d\n",k);


    return 0;
}

int get(char *s,int k,int l){
    int i,tmp;

    for (i = 0;i < l;i++) {
        if(s[i]=='B'&&s[i+1]=='W'){
            tmp=s[i];
            s[i]=s[i+1];
            s[i+1]=tmp;
            printf("%s\n",s);
            k++;
        }
    }
    if(l%2==0){
        for(i=0;i<l/2;i++){
            if(s[i]=='B'){
                k=get(s,k,l);
                break;
            }
        }    
    }
    else{
        for(i=0;i<l/2+1;i++){
            if(s[i]=='B'){
                k=get(s,k,l);
                break;
            }
        }
    }
    return k;

}