N, M = map(int, input().split())
S = [input() for _ in range(N)]

for i in range(N):
    bit = 0
    for j in range(M):
        bit |= 1<<j if S[i][j] == "o" else 0
    S[i] = bit

F = [False]*(1<<N)
for bit in range(1<<N):
    b = (1<<M)-1
    for i in range(N):
        if 1<<i & bit:
            b &= S[i]
    if b.bit_count() == 1:
        F[bit] = True

dp = [0]*(1<<N)
dp[0] = 1
ans = 0
for bit in range(1<<N):
    if F[bit]:
        ans += bit.bit_count()*dp[bit]
        continue
    rem = N-bit.bit_count()
    for i in range(N):
        if not 1<<i & bit:
            dp[bit|1<<i] += dp[bit]/rem

print(ans)