#include <iostream>
using namespace std;

template <int MOD>
struct StaticModint
{
    using mint = StaticModint;

public:
    int val;

    StaticModint() : val(0) {}

    StaticModint(long long v)
    {
        if (std::abs(v) >= mod())
        {
            v %= mod();
        }
        if (v < 0)
        {
            v += mod();
        }
        val = v;
    }

    mint &operator++()
    {
        val++;
        if (val == mod())
        {
            val = 0;
        }
        return *this;
    }

    mint &operator--()
    {
        if (val == 0)
        {
            val = mod();
        }
        val--;
        return *this;
    }

    mint &operator+=(const mint &x)
    {
        val += x.val;
        if (val >= mod())
        {
            val -= mod();
        }
        return *this;
    }

    mint &operator-=(const mint &x)
    {
        val -= x.val;
        if (val < 0)
        {
            val += mod();
        }
        return *this;
    }

    mint &operator*=(const mint &x)
    {
        val = (int)((long long)val * x.val % mod());
        return *this;
    }

    mint &operator/=(const mint &x)
    {
        *this *= x.inv();
        return *this;
    }

    mint operator-()
    {
        return mint() - *this;
    }

    mint pow(long long n) const
    {
        mint x = 1, r = *this;
        while (n)
        {
            if (n & 1)
            {
                x *= r;
            }
            r *= r;
            n >>= 1;
        }
        return x;
    }

    mint inv() const
    {
        return pow(mod() - 2);
    }

    friend mint operator+(const mint &x, const mint &y)
    {
        return mint(x) += y;
    }

    friend mint operator-(const mint &x, const mint &y)
    {
        return mint(x) -= y;
    }

    friend mint operator*(const mint &x, const mint &y)
    {
        return mint(x) *= y;
    }

    friend mint operator/(const mint &x, const mint &y)
    {
        return mint(x) /= y;
    }

    friend bool operator==(const mint &x, const mint &y)
    {
        return x.val == y.val;
    }

    friend bool operator!=(const mint &x, const mint &y)
    {
        return x.val != y.val;
    }

    friend std::ostream &operator<<(std::ostream &os, const mint &x)
    {
        return os << x.val;
    }

    friend std::istream &operator>>(std::istream &is, mint &x)
    {
        long long v;
        is >> v;
        x = mint(v);
        return is;
    }

private:
    static constexpr int mod()
    {
        return MOD;
    }
};

using mint = StaticModint<998244353>;

const int r[4] = {0, 2, 3, 1};

int main()
{
    int n, m;
    cin >> n >> m;
    string s[505];
    for(int i = 0; i < n; i++)
    {
        cin >> s[i];
    }
    mint ep[4];
    ep[0] = 1;
    for(int i = 0; i < n; i++)
    {
        mint dp[4];
        dp[0] = 1;
        for(int j = 0; j < m; j++)
        {
            mint d[4];
            for(int o = 0; o < 2; o++)
            {
                if(s[i][j] != 'W')
                {
                    d[o * 2 + 1] += dp[o];
                }
                if(s[i][j] != 'B')
                {
                    d[o * 2] += dp[o];
                }
            }
            for(int o = 2; o < 4; o++)
            {
                if(s[i][j] != 'W')
                {
                    d[3 - ((o * 2 + 1) & 3)] += dp[o];
                }
                if(s[i][j] != 'B')
                {
                    d[3 - ((o * 2) & 3)] += dp[o];
                }
            }
            swap(dp, d);
        }
        mint e[4];
        for(int x = 0; x < 4; x++)
        {
            for(int y = 0; y < 4; y++)
            {
                e[r[x ^ y]] += ep[x] * dp[y];
            }
        }
        swap(ep, e);
    }
    cout << ep[0] << endl;
}