mod = 998244353
def main():
    h, w = list(map(int, input().split()))
    S = [input() for _ in range(h)]
    X = [[0, 0, 0, 0] for _ in range(h)]
    for y in range(h):
        dp = [0] * 4
        dp[0] = 1
        for x in range(w):
            ndp = [0] * 4
            if S[y][x] != "B":
                for bit in range(4):
                    nbit = bit * 2
                    if 4 <= nbit:
                        nbit ^= 3
                    nbit = nbit % 4
                    ndp[nbit] = (ndp[nbit] + dp[bit]) % mod
            if S[y][x] != "W":
                for bit in range(4):
                    nbit = (bit^2) * 2
                    if 4 <= nbit:
                        nbit ^= 3
                    nbit = nbit % 4
                    ndp[nbit] = (ndp[nbit] + dp[bit]) % mod
            dp = ndp
        X[y] = dp
    dp = [0] * 4
    dp[0] = 1
    for y in range(h):
        ndp = [0] * 4
        for i in range(4):
            for j in range(4):
                k = i^j
                if k == 0:
                    v = 0
                elif k == 1:
                    v = 2
                elif k == 2:
                    v = 3
                else:
                    v = 1
                ndp[v] = (ndp[v] + dp[i]*X[y][j]) % mod
        dp = ndp
    return dp[0]

print(main())