# -*- coding:utf-8 -*-
from heapq import heappop, heappush

if __name__ == "__main__":
	w,h = map(int,raw_input().split())
	c = [raw_input()for i in range(h)]
	arrived = [[False for i in xrange(w)]for j in xrange(h)]
	direc = [(1,0),(-1,0),(0,1),(0,-1)]
	for i in xrange(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 direc:
						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))