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: Time Limit Exceeded)

#ifndef LOCAL
#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#else
#include <iostream>
#include <iomanip> 
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <memory>
#include <cctype>
#include <cstring>
#include <vector>
#include <list>
#include <queue>
#include <deque>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <numeric>
#include <unordered_map>
#include <unordered_set>
#endif
using namespace std;
#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; }; sim > rge<c> range(c i, c j) { return rge<c>{i, j}; } sim > auto dud(c* x) -> decltype(cerr << *x, 0); sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; } eni(!=) cerr << boolalpha << i; ris; } eni(==) ris << range(begin(i), end(i)); } sim, class b dor(pair < b, c > d) { ris << "(" << d.first << ", " << d.second << ")"; } sim dor(rge<c> d) { *this << "["; for (auto it = d.b; it != d.e; ++it) *this << ", " + 2 * (it == d.b) << *it; ris << "]"; }
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "

// #include <ext/pb_ds/assoc_container.hpp> 
// #include <ext/pb_ds/tree_policy.hpp> 
// using namespace __gnu_pbds; 
// #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> 

template<typename T> void setmax(T& x, T y) {x = max(x, y);}
template<typename T> void setmin(T& x, T y) {x = min(x, y);}
#define fix(a) fixed << setprecision(a)
#define forn(i, n) for (int i = 0; i < int(n); i++)
#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
#define all(V) V.begin(), V.end()
#define rall(V) V.rbegin(), V.rend()
#define len(V) (int)V.size()
#define ll long long
#define ld long double
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define endl '\n'


void solve(){ 
  string s;
  cin >> s;
  int n = len(s);
  int ans = 0;
  forn(i,n)forn(j,n-1){
    if (s[j] < s[j + 1]) ans++,swap(s[j], s[j+1]);
  }
  cout << ans << endl;
}

int main() {
  ios::sync_with_stdio(false);
  int t = 1;
  // cin >> t;
  forn(i, t){
    solve();
  }
}

/* 

6
1 1
7 1
2 2
6 2
1 3
7 3

0 < 2 > 1 > 0

 */