def color(s,c,h,w)
	def dfs(s,c,x,y)
		s[x][y]=c
		[[1,0],[0,1],[-1,0],[0,-1]].each{|dx,dy|
			nx=x+dx
			ny=y+dy
			dfs(s,c,nx,ny) if s[nx][ny]==?.
		}
	end

	h.times{|i|w.times{|j|
		if s[i][j]==?.
			dfs(s,c,i,j)
			return true
		end
	}}
	false
end

def dist(p1,p2)
	(p1[0]-p2[0]).abs+(p1[1]-p2[1]).abs-1
end

def min_dist(pts1,pts2)
	ret=1<<30
	pts1.each{|p1|pts2.each{|p2|
		d=dist(p1,p2)
		ret=d if d<ret
	}}
	ret
end

w,h=gets.split.map(&:to_i)
space=h.times.map{gets.chomp.chars.to_a}

color(space,?1,h,w)
color(space,?2,h,w)

pts1=[]
pts2=[]

space.each_with_index{|r,x|r.each_with_index{|c,y|
	if c==?1
		pts1<<[x,y]
	elsif c==?2
		pts2<<[x,y]
	end
}}

p min_dist(pts1,pts2)
#puts space.map(&:join)