integer(kind=2)::H,W
  character,allocatable::map(:,:)
  character,parameter::riku='#',umi='.'
  logical,allocatable::covered(:,:)
  character*3000::string
  integer::cdist

  read *,H,W
  allocate(map(0:W+1,0:H+1))
  allocate(covered(0:W+1,0:H+1))

  do i=1,H
     read *, string
     do j=1,W
        map(j,i)=string(j:j)
     end do
  end do

  map(0  ,:)  =umi
  map(W+1,:)  =umi
  map(:  ,0)  =umi
  map(:,H+1)  =umi

  cdist=1
  do i=1,W
     do j=1,H
        if(map(i,j).eq.riku) then
           do l=1,MAX(H,W)
              if(ANY(map(MIN(i+l,W+1),MAX(0,j-l):MIN(j+l,H+1)).eq.umi) .or. &
                 ANY(map(MAX(i-l,0),  MAX(0,j-l):MIN(j+l,H+1)).eq.umi) .or. &
                 ANY(map(MAX(0,i-l):MIN(i+l,W+1),MIN(j+l,H+1)).eq.umi) .or. &
                 ANY(map(MAX(0,i-l):MIN(i+l,W+1),MAX(j-l,0))  .eq.umi) ) then
                 cdist = MAX(cdist,l)
                 exit
              end if
           end do
        end if
     end do
  end do
  print '(i0)',cdist
end program