n,m=gets.split.map &:to_i
a=(1..m).map{gets}
(0...m).any?{|x|(0...n).any?{|y|q=(b=a[x][y]==?.)?[x,y]:[]
(x=q.shift
y=q.shift
m.times{|z|n.times{|w|(a[z][w]=?!;q+=[z,w])if (x-z).abs+(y-w).abs<2&&a[z][w]==?.}})while[]!=q
b}}
c=99
m.times{|x|n.times{|y|m.times{|z|n.times{|w|c=[c,(x-z).abs+(y-w).abs-1].min if a[x][y]==?!&&a[z][w]==?.}}}}
p c