#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <math.h>
#include <queue>
#include <numeric>
#include <iomanip>
using namespace std;

using ll = long long;

#define For(i,a,b) for(ll i=(a);i<(ll)(b);i++)
#define rFor(i,a,b) for(ll i=(a);i>=(ll)(b);i--)
#define co(a) cout<<a<<endl
#define Sort(a) sort((a).begin(),(a).end())
#define Rev(a) reverse((a).begin(),(a).end())
#define Unique(a) (a).erase(unique((a).begin(), (a).end()),(a).end())
#define cfs(a) cout<<fixed<<setprecision(a) 


int main() {
	ll H, W;
	cin >> H >> W;
	vector<string> s(H);
	For(i, 0, H) {
		cin >> s[i];
	}
	ll N = H + W - 1;
	ll is;
	ll h, w;
	ll ans = 1;
	bool end = false;
	For(i, 0, N) {
		is = -1;
		h = 0;
		w = i;
		if (w >= W) {
			h = i % W + 1 + (i / W - 1) * W;
			w = W - 1;
		}
		for (;;) {
			if (s[h][w] == 'R') {
				if (is != 1) {
					is = 0;
				}
				else {
					end = true;
					break;
				}
			}
			else if (s[h][w] == 'B') {
				if (is != 0) {
					is = 1;
				}
				else {
					end = true;
					break;
				}
			}
			h++;
			w--;
			if (h >= H || w < 0) {
				if (is == -1) {
					ans *= 2;
					ans %= 998244353;
					//co(h << " " << w << " " << ans<<" "<<i);
				}
				break;
			}
		}
	}
	if (end) {
		co(0);
	}
	else {
		co(ans);
	}
}
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n)  for(long long i=0;i<(long long)(n);i++)
#define REP(i,k,n) for(long long i=k;i<(long long)(n);i++)
#define pb emplace_back
#define lb(v,k) (lower_bound(all(v),(k))-v.begin())
#define ub(v,k) (upper_bound(all(v),(k))-v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T,vector<T>,greater<T>>
#define dame(a) {out(a);return 0;}
#define decimal cout<<fixed<<setprecision(15);
#define all(a) a.begin(),a.end()
#define rsort(a) {sort(all(a));reverse(all(a));}
#define dupli(a) {sort(all(a));a.erase(unique(all(a)),a.end());}
typedef long long ll;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> PP;
typedef tuple<ll,ll,ll,ll> PPP;
using vi=vector<ll>;
using vvi=vector<vi>;
using vvvi=vector<vvi>;
using vvvvi=vector<vvvi>;
using vp=vector<P>;
using vvp=vector<vp>;
using vb=vector<bool>;
using vvb=vector<vb>;
const ll inf=1001001001001001001;
const ll INF=1001001001;
const ll mod=998244353;
const double eps=1e-10;
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outp(T a){cout<<'('<<a.fi<<','<<a.se<<')'<<'\n';}
template<class T> void outvp(T v){rep(i,v.size())cout<<'('<<v[i].fi<<','<<v[i].se<<')';cout<<'\n';}
template<class T> void outvvp(T v){rep(i,v.size())outvp(v[i]);}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){rep(i,v.size())outv(v[i]);}
template<class T> bool isin(T x,T l,T r){return (l)<=(x)&&(x)<=(r);}
template<class T> void yesno(T b){if(b)out("yes");else out("no");}
template<class T> void YesNo(T b){if(b)out("Yes");else out("No");}
template<class T> void YESNO(T b){if(b)out("YES");else out("NO");}
template<class T> void outset(T s){auto itr=s.begin();while(itr!=s.end()){if(itr!=s.begin())cout<<' ';cout<<*itr;itr++;}cout<<'\n';}
void outs(ll a,ll b){if(a>=inf-100)out(b);else out(a);}
ll gcd(ll a,ll b){if(b==0)return a;return gcd(b,a%b);}
ll modpow(ll a,ll b){ll res=1;a%=mod;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res;}

int main(){
    ll h,w;cin>>h>>w;
    vector<string> v(h);rep(i,h)cin>>v[i];
    vvi cnt(h+w,vi(3));
    rep(i,h)rep(j,w){
        if(v[i][j]=='R')cnt[i+j][0]++;
        if(v[i][j]=='B')cnt[i+j][1]++;
        if(v[i][j]=='.')cnt[i+j][2]++;
    }
    ll ans=1;
    rep(i,h+w){
        if(cnt[i][0]&&cnt[i][1])dame(0);
        if(cnt[i][0]||cnt[i][1])continue;
        if(cnt[i][2])ans=ans*2%mod;
    }
    out(ans);
}