h,w=map(int,input().split()) X=[] ans=100000 for i in range(h): s=input() X.append(s) cnt=0 for j in s: if j=="." and cnt!=0: ans=min(ans,cnt) cnt=0 if j=="#": cnt+=1 if cnt!=0: ans=min(ans,cnt) for i in range(w): cnt=0 for j in range(h): key=X[j][i] if key=="." and cnt!=0: ans=min(ans,cnt) cnt=0 if key=="#": cnt+=1 if cnt!=0: ans=min(ans,cnt) print(ans)