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: Wrong Answer)

#include<bits/stdc++.h>
using   namespace   std;
#define N  200010
#define LL  long    long
char    a[N];
int main()
{
    int i,j,k;
    LL  s1,s2,s3,s4,s;
    scanf("%s",a+1);
    k=strlen(a+1);
    s=0;
    s1=0;
    for(i=1;i<=k;i++)
    {
        if(a[i]=='B')
            s++;
        else
            s1=s1+s;
    }
    s=0;
    s2=0;
    for(i=1;i<=k;i++)
    {
        if(a[i]=='W')
            s++;
        else
            s2=s2+s;
    }
    s=0;
    s3=0;
    for(i=k;i>=1;i--)
    {
        if(a[i]=='B')
            s++;
        else
            s3=s3+s;
    }
    s=0;
    s4=0;
    for(i=k;i>=1;i--)
    {
        if(a[i]=='W')
            s++;
        else
            s4=s4+s;
    }
    s=max(s1,s2);
    s=max(s,s3);
    s=max(s,s4);
    printf("%lld\n",s);
    return  0;
}