from heapq import heappop,heappush
W,H=map(int,raw_input().split())
C=[raw_input() for i in range(H)]
arrived=[[False for i in range(W)] for j in range(H)]
directions=[(1,0),(-1,0),(0,1),(0,-1)]
for i in range(H):
    for j in range(W):
        if C[i][j] =='.':
            hp=[]
            heappush(hp,(0,i,j))
            arrived[i][j]=True
            while len(hp)!=0:
                (d,a,b)=heappop(hp)
                if d > 0 and C[a][b] == '.':
                    print d
                    exit()
                for da,db in directions:
                    na=a+da
                    nb=b+db
                    nd=d
                    if na>=0 and nb >= 0 and na <H and nb <W and arrived[na][nb]==False:
                        if C[na][nb]=='#':
                            nd+=1
                        arrived[na][nb]=True
                        heappush(hp,(nd,na,nb))