#include <bits/stdc++.h>
#define rep(i, p, n) for (ll i = p; i < (ll)(n); i++)
#define rep2(i, p, n) for (ll i = p; i >= (ll)(n); i--)
using namespace std;
using ll = long long;
using ld = long double;
const double pi = 3.141592653589793;
const long long inf = 2 * 1e9;
const long long linf = 4 * 1e18;
const ll mod1 = 1000000007;
const ll mod2 = 998244353;
template <class T>
inline bool chmax(T &a, T b)
{    if (a < b)    {        a = b;        return 1;    }    return 0;}
template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return 1;
    }
    return 0;
}

//atcoder
#include <atcoder/all>
using namespace atcoder;
using mint1 = modint1000000007;
using mint2 = modint998244353;

vector<pair<ll, ll>> base={{-1, 0}, {1, 0}, {0, -1}, {0, 1}};

ll N, M;

bool calc(vector<string> S) {
    vector<vector<bool>> G(N, vector<bool>(M));
    rep(i, 0, N) {
    	rep(j, 0, M) {
    		if (S.at(i).at(j)=='B') {
    			G.at(i).at(j)=true;
    		}
    	}
    }
    rep(i, 0, N) {
        rep2(j, M-1, 0) {
            if (!G.at(i).at(j)) {
                continue;
            }
            if (i<N-2) {
                rep(k, 0, 3) {
                    G.at(i+k).at(j)=!G.at(i+k).at(j);
                }
            }
            else if (j>1) {
                rep(k, 0, 3) {
                    G.at(i).at(j-k)=!G.at(i).at(j-k);
                }
            }
            else if (i==N-2 && j==1) {
                G.at(i).at(j)=!G.at(i).at(j);
                G.at(i+1).at(j)=!G.at(i+1).at(j);
                G.at(i).at(j-1)=!G.at(i).at(j-1);
            }
            else if (i==N-2) {
                G.at(i).at(j)=!G.at(i).at(j);
                G.at(i+1).at(j)=!G.at(i+1).at(j);
                G.at(i+1).at(j+1)=!G.at(i+1).at(j+1);
            }
        }
    }
    if (!G.at(N-1).at(0) && !G.at(N-1).at(1)) {
        return true;
    }
    else {
        return false;
    }
}

int main() {
    cin >> N >> M;
    vector<string> S(N);
    rep(i, 0, N) {
        cin >> S.at(i);
    }
    ll co=0;
    mint2 ans=1;
    ll x, y;
    rep(i, 0, N) {
        rep(j, 0, M) {
            if (S.at(i).at(j)=='?') {
                co++;
                x=i;
                y=j;
            }
        }
    }
    if (co>=2) {
        rep(i, 0, co) {
            ans*=2;
        }
        ans/=4;
        cout << ans.val();
    }
    else if (co==1) {
        S.at(x).at(y)='W';
        if (calc(S)) {
            cout << 1;
            return 0;
        }
        S.at(x).at(y)='B';
        if (calc(S)) {
            cout << 1;
            return 0;
        }
        cout << 0;
    }
    else {
        if (calc(S)) {
            cout << 1;
        }
        else {
            cout << 0;
        }
    }
}