# include <bits/stdc++.h>
# include <atcoder/modint>
# include <atcoder/segtree>
# include <atcoder/lazysegtree>
# include <atcoder/dsu>
# include <atcoder/scc>
# include <atcoder/string>
# include <atcoder/twosat>
# include <atcoder/math>
# include <atcoder/convolution>
//# include <regex>

using namespace std;
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<vector<int>>> vvvi;
typedef vector<long long> vl;
typedef vector<vector<long long>> vvl;
typedef vector<vector<vector<long long>>> vvvl;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vector<vector<bool>>> vvvb;
#define rep(i,n) for(int i=0;i<n;i++)
#define reps(i,m,n) for(int i=m;i<n;i++)
#define repl(i,n) for(ll i=0;i<n;i++)
#define repsl(i,m,n) for(ll i=m;i<n;i++)
#define repr(i,n) for(int i=n-1;i>=0;i--)
#define repsr(i,m,n) for(int i=n-1;i>=m;i--)
#define replr(i,n) for(ll i=n-1;i>=0;i--)
#define repslr(i,m,n) for(ll i=n-1;i>=m;i--)
#define sksort(x) sort(x.begin(), x.end())
#define sksortr(x) sort(x.rbegin(), x.rend())
#define disp(x) cout << x << endl
#define disps(x) cout << x << " "
#define dispe cout << endl
#define dispv(x) for(ll xqzj=0;xqzj<(ll)x.size();xqzj++){disps(x[xqzj]);}dispe
#define dispvv(x) for(ll xqzi=0;xqzi<(ll)x.size();xqzi++){dispv(x[xqzi]);}
#define dispvm(x) for(ll xqzj=0;xqzj<(ll)x.size();xqzj++){disps(x[xqzj].val());}dispe
#define dispvvm(x) for(ll xqzi=0;xqzi<(ll)x.size();xqzi++){dispvm(x[xqzi]);}
#define dispy cout << "Yes" << endl
#define dispn cout << "No" << endl
#define dispyn(x) if(x)dispy;else dispn
#define dispd cout << std::setprecision(20)
#define inp(x) int x;cin>>x
#define inpl(x) ll x;cin>>x
#define inps(x) string x;cin>>x
#define allv(x)  (x).begin(),(x).end()
#define allrv(x)  (x).rbegin(),(x).rend()
#define imax(x,y) x=max(x,y)
#define imin(x,y) x=min(x,y)
#define perm(x,y) vi permv(x);rep(permi,x)permv[permi]=permi;do y while(next_permutation(allv(permv)))
template <class T>
using priority_queue_asc = std::priority_queue<T,std::vector<T>,std::greater<T>>;
using mint = atcoder::modint998244353;
//using mint = atcoder::modint1000000007;

#ifndef ATCODER_COMBINATION_HPP
#define ATCODER_COMBINATION_HPP 1

#include <vector>

namespace atcoder {

// Reference: https://ei1333.github.io/luzhiled/snippets/math/combination.html

template<typename T>
struct Combination {
    std::vector<T> _fact, _rfact, _inv;

    explicit Combination(int sz) : _fact(sz + 1), _rfact(sz + 1), _inv(sz + 1) {
        _fact[0] = _rfact[sz] = _inv[0] = 1;
        for(int i = 1; i <= sz; i++) _fact[i] = _fact[i - 1] * i;
        _rfact[sz] /= _fact[sz];
        for(int i = sz - 1; i >= 0; i--) _rfact[i] = _rfact[i + 1] * (i + 1);
        for(int i = 1; i <= sz; i++) _inv[i] = _rfact[i] * _fact[i - 1];
    }

    inline T fact(int k) const { return _fact[k]; }

    inline T rfact(int k) const { return _rfact[k]; }

    inline T inv(int k) const { return _inv[k]; }

    T P(int n, int r) const {
        if(r < 0 || n < r) return 0;
        return fact(n) * rfact(n - r);
    }

    T C(int p, int q) const {
        if(q < 0 || p < q) return 0;
        return fact(p) * rfact(q) * rfact(p - q);
    }

    T H(int n, int r) const {
        if(n < 0 || r < 0) return (0);
        return r == 0 ? 1 : C(n + r - 1, r);
    }
};

}  // namespace atcoder

#endif  // ATCODER_COMBINATION_HPP

int main(){
    inps(s);
    int n=s.size();
    int b=0;
    rep(i,n)if(s[i]=='B')b++;
    mint ans=1;
    atcoder::Combination<mint> cb(n);
    rep(i,n)if(s[i]=='B'){
        ans+=cb.C(n-i-1,b);
        b--;
    }
    disp(ans.val());
}