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>
#include<string.h>

#define MAX 200000

void run(){
  char S[MAX+1];
  scanf(" %s", S);
  signed int len = strlen(S);
  char *a = S;
  int n = -1, cnt = 0, ans = 0;
  while(n!=len-1){
    while(a[++n] != 'W' && n <= len-1) cnt++;
    if(n == 0) continue;
    if(a[n-1] == 'B'){
      a[n] = 'B'; a[n-1] = 'W';
      ans += cnt;
    }
    
  }
  printf("%d\n", ans);
}
int main(){
  run();
  return 0;
}