integer(kind=4)::H,W
  character,allocatable::map(:,:)
  character,parameter::riku='#',umi='.'
  integer,allocatable::rcdist(:,:)
  character*3000::string
  integer::cdist,min_cdist,max_cdist

  read *,H,W

  allocate(map(0:W+1,0:H+1))
  allocate(rcdist(1:W,1:H))

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

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

  do i=1,W
     do j=1,H
        if (map(i,j).eq.umi) then
           continue
        end if

        do k=1,MIN(MIN(W+1-i,i),MIN(H+1-j,j))
           if     (ANY(map(i+k,j-k:j+k).eq.umi)) then
              rcdist(i,j)=k
              exit
           else if(ANY(map(i-k,j-k:j+k).eq.umi)) then
              rcdist(i,j)=k
              exit
           else if(ANY(map(i-k+1:i+k-1,j+k).eq.umi)) then
              rcdist(i,j)=k
              exit
           else if(ANY(map(i-k+1:i+k-1,j-k).eq.umi)) then
              rcdist(i,j)=k
              exit
           end if
        end do

     end do
  end do

  max_cdist=0
  do i=1,W
     do j=1,H
        if(map(i,j).eq.riku) then
           max_cdist=MAX(max_cdist, rcdist(i,j))
        end if
     end do
  end do
  print '(i0)',max_cdist
end program