#include <bits/stdc++.h>
using namespace std;

#include <atcoder/modint>
using mint = atcoder::modint998244353;

int main() {
  int N, M;
  cin >> N >> M;
  vector<string> S(N);
  for(int i = 0; i < N; i++) {
    cin >> S[i];
  }
  vector<int> cnt_q(N + M - 1);
  vector<int> cnt_b(N + M - 1);
  for(int i = 0; i < N; i++) {
    for(int j = 0; j < M; j++) {
      cnt_q[i + j] += (S[i][j] == '?');
      cnt_b[i + j] += (S[i][j] == 'B');
    }
  }
  vector dp(N + M - 1, vector<mint>(4));
  for(int f0 : {0, 1}) for(int f1 : {0, 1}) {
    if(cnt_q[0] == 0 && f0 != cnt_b[0] % 2) continue;
    if(cnt_q[1] == 0 && f1 != cnt_b[1] % 2) continue;
    dp[1][(f0 << 0) | (f1 << 1)] = mint(2).pow(max(0, cnt_q[0] - 1) + max(0, cnt_q[1] - 1));
  }
  for(int i = 2; i < N + M - 1; i++) {
    for(int f0 : {0, 1}) for(int f1 : {0, 1}) for(int f2 : {0, 1}) {
      if(cnt_q[i] == 0 && f2 != cnt_b[i] % 2) continue;
      dp[i][((f1 ^ f0) << 0) | ((f2 ^ f0) << 1)] += dp[i - 1][(f0 << 0) | (f1 << 1)] * mint(2).pow(max(0, cnt_q[i] - 1));
    }
  }
  cout << dp.back()[0].val() << endl;
}