#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;
using mint = atcoder::modint998244353;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    string s;
    cin >> s;
    while(!s.empty() && s.back() == 'B') s.pop_back();
    if(s.empty()){
        cout << "1\n";
        return 0;
    }
    int n = s.size();
    reverse(s.begin(), s.end());
    vector<mint> tb(n + 1);
    tb[0] = 1;
    int l = 0, r = 0;
    for(int i = 0; i < n; i++){
        for(int j = r; j >= l; j--) tb[j + 1] += tb[j];
        r++;
        if(s[i] == 'B') l++;
    }
    cout << tb[l].val() << '\n';
}