#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<vvvl> vvvvl;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<vvb> vvvb;
typedef vector<vvvb> vvvvb;
typedef pair<ll,ll> pl;
typedef pair<ll,pl> ppl;
typedef pair<ll,ppl> pppl;
typedef pair<ll,pppl> pppppl;
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(a) begin(a),end(a)
#define sz(a) (int)(a).size()
#define F first
#define S second
#define bs(A,x) binary_search(all(A),x)
#define lb(A,x) (ll)(lower_bound(all(A),x)-A.begin())
#define ub(A,x) (ll)(upper_bound(all(A),x)-A.begin())
#define cou(A,x) (ll)(upper_bound(all(A),x)-lower_bound(all(A),x))
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
template<class T>bool chmax(T&a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T&a,T b){if(b<a){a=b;return 1;}return 0;}
//*
using mint=modint998244353;
const ll mod=998244353;
//*/
/*
using mint=modint1000000007;
const ll mod=1000000007;
//*/
//using mint=modint;
//*
typedef vector<mint> vm;
typedef vector<vm> vvm;
typedef vector<vvm> vvvm;
typedef vector<vvvm> vvvvm;
ostream&operator<<(ostream&os,mint a){os<<a.val();return os;}
istream&operator>>(istream&is,mint&a){int x;is>>x;a=mint(x);return is;}
//*/
template<typename T1,typename T2>ostream&operator<<(ostream&os,pair<T1,T2>p){os<<p.F<<" "<<p.S;return os;}
template<typename T1,typename T2>istream&operator>>(istream&is,pair<T1,T2>&p){is>>p.F>>p.S;return is;}
template<typename T>ostream&operator<<(ostream&os,vector<T>v){rep(i,0,sz(v))os<<v[i]<<(i+1!=sz(v)?" ":"");return os;}
template<typename T>istream&operator>>(istream&is,vector<T>&v){for(T&in:v)is>>in;return is;}
int main(){
  cin.tie(0)->sync_with_stdio(0);
  cin.exceptions(cin.failbit);
  string S;cin>>S;
  ll N=sz(S);
  vl A(N+1),B(N+1);
  rep(i,0,N)A[i+1]=A[i]+(S[i]=='A');
  rep(i,0,N)B[i+1]=B[i]+(S[i]=='B');
  vm ex(2e6,1),re(2e6);
  rep(i,1,2e6)ex[i]=i*ex[i-1];
  rep(i,0,2e6)re[i]=1/ex[i];
  //https://kanpurin.hatenablog.com/entry/2021/09/15/220913#aruryoiki
  function<vm(ll,ll,vm&)>dc=[&](ll l,ll r,vm&bottom){
  	if(r-l==1){
  		if(S[l]=='A')return vm{bottom[1]};
  		else return vm{bottom[0],bottom[0]};
  	}
  	ll m=(l+r)/2;
  	vm left(A[m]-A[l]+1),right(A[r]-A[m]+1);
  	rep(i,A[l],A[m]+1)left[i-A[l]]=bottom[i-A[l]];
  	rep(i,A[m],A[r]+1)right[i-A[m]]=bottom[i-A[l]];
  	auto X=dc(l,m,left);
  	ll H=sz(X)-1,W=sz(right)-1;
  	vm top(W+1),res(H+1);
  	
  	res[0]=right[W];
  	top[0]=X[H];
  	X[0]=right[0]=0;
  	
  	if(W==0)rep(i,1,H+1)res[i]=X[i];
  	else{
	  	vm F(H+1);
	  	rep(i,0,H+1)F[i]=ex[i+W-1]*re[W-1]*re[i];
	  	auto G=convolution(X,F);
	  	rep(i,1,H+1)res[i]+=G[i];
	  	rep(i,0,H+W+1)F[i]=ex[i];
	  	rep(i,0,W+1)right[i]*=re[W-i];
	  	G=convolution(F,right);
	  	rep(i,0,W+1)right[i]*=ex[W-i];
	  	rep(i,1,H+1)res[i]+=re[i-1]*G[i+W-1];
  	}
  	
  	swap(H,W);
  	swap(X,right);
  	
  	if(W==0)rep(i,1,H+1)top[i]=X[i];
  	else{
	  	vm F(H+1);
	  	rep(i,0,H+1)F[i]=ex[i+W-1]*re[W-1]*re[i];
	  	auto G=convolution(X,F);
	  	rep(i,1,H+1)top[i]+=G[i];
	  	rep(i,0,H+W+1)F[i]=ex[i];
	  	rep(i,0,W+1)right[i]*=re[W-i];
	  	G=convolution(F,right);
	  	rep(i,0,W+1)right[i]*=ex[W-i];
	  	rep(i,1,H+1)top[i]+=re[i-1]*G[i+W-1];
  	}
  	
  	auto Y=dc(m,r,top);
  	Y.erase(Y.begin());
  	res.insert(res.end(),all(Y));
  	return res;
  };
  vm bottom(A[N]+1,1);
  auto ans=dc(0,N,bottom);
  cout<<ans.back()<<endl;
  return 0;
}