h, w = map(int, input().split())
s = [input() for i in range(h)]

assert 3 <= h <= 500 and 3 <= w <= 500
for i in range(h):
    for j in range(w):
        assert s[i][j] in ["W", "B", "?"]

q_cnt = [0] * 3
b_cnt = [0] * 3
mod = 998244353

for i in range(h):
    for j in range(w):
        if s[i][j] == "B":
            b_cnt[(i + j) % 3] += 1
        if s[i][j] == "?":
            q_cnt[(i + j) % 3] += 1


ans_o = 1
ans_e = 1
for b, q in zip(b_cnt, q_cnt):
    if b & 1:
        ans_e *= 0 if not q else pow(2, q - 1, mod)
        ans_o *= 1 if not q else pow(2, q - 1, mod)
    else:
        ans_e *= 1 if not q else pow(2, q - 1, mod)
        ans_o *= 0 if not q else pow(2, q - 1, mod)

    ans_e %= mod
    ans_o %= mod

print((ans_e + ans_o) % mod)