#include <atcoder/modint>
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using mint = atcoder::modint998244353;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void solve() {
  ll h, w;
  cin >> h >> w;
  vector<mint> dp1(4, 0);
  dp1[0] = 1;
  rep(i, h) {
    string s;
    cin >> s;
    vector<mint> dp2(4, 0);
    dp2[0] = 1;
    rep(j, w - 2) {
      vector<mint> nex(4, 0);
      rep(pk, 4) {
        ll nk1 = pk >> 1;
        ll nk2 = ((~pk) >> 1) & 3;
        if (s[j] == 'B' || s[j] == '?') {
          if ((pk & 1) == 1) {
            nex[nk1] += dp2[pk];
          } else {
            nex[nk2] += dp2[pk];
          }
        }
        if (s[j] == 'W' || s[j] == '?') {
          if ((pk & 1) == 0) {
            nex[nk1] += dp2[pk];
          } else {
            nex[nk2] += dp2[pk];
          }
        }
      }
      swap(dp2, nex);
    }
    vector<mint> nex(4, 0);
    const vector<ll> fs = {0, 3, 1, 2};
    rep(k1, 4) rep(k2, 4) {
      ll flip = k2 ^ fs[k1];
      rep(pk, 4) {
        bool ok = true;
        rep(j, 2) {
          if (s[w - 2 + j] == 'B') {
            ok &= ((pk >> j) & 1) == 1;
          }
          if (s[w - 2 + j] == 'W') {
            ok &= ((pk >> j) & 1) == 0;
          }
        }
        if (ok) {
          ll nk = pk ^ flip;
          nex[nk] += dp1[k1] * dp2[k2];
        }
      }
    }
    swap(dp1, nex);
  }
  cout << dp1[0].val() << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}