#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();
    int n = s.size();
    reverse(s.begin(), s.end());
    vector<vector<mint>> tb(n);
    vector<pair<int,int>> rng(n);
    for(int i = 0; i < n; i++){
        if(s[i] == 'A'){
            tb[i] = {1, 1};
            rng[i] = make_pair(0, 1);
        }else{
            tb[i] = {1, 1};
            rng[i] = make_pair(-1, 0);
        }
    }
    auto dfs = [&](auto dfs, int l, int r) -> void {
        if(r - l <= 1) return;
        int mid = (l + r) / 2;
        dfs(dfs, l, mid);
        dfs(dfs, mid, r);
        tb[l] = atcoder::convolution(tb[l], tb[mid]);
        rng[l] = make_pair(rng[l].first + rng[mid].first, rng[l].second + rng[mid].second);
        if(l == 0){
            reverse(tb[l].begin(), tb[l].end());
            while(rng[l].first < 0){
                rng[l].first++;
                tb[l].pop_back();
            }
            reverse(tb[l].begin(), tb[l].end());
        }
    };
    dfs(dfs, 0, n);
    cout << tb[0][0].val() << '\n';
}