import sys
input = sys.stdin.readline

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

A=[]
for s in S:
    x=0
    for i in range(len(s)):
        if s[i]=="o":
            x|=(1<<i)

    A.append(x)

DP=[0]*(1<<N)
DP[0]=1

ANS=0
for i in range(1<<N):
    if DP[i]==0:
        continue
    now=(1<<M)-1
    for j in range(N):
        if i & (1<<j) != 0:
            now=now&A[j]

    if now.bit_count()==1:
        ANS+=DP[i]*(i.bit_count())
        DP[i]=0
    else:            
        x=N-(i.bit_count())

        for j in range(N):
            if i&(1<<j)!=0:
                continue

            to=i|(1<<j)
            DP[to]+=DP[i]/x


print(ANS)