integer(kind=4)::H,W
  logical,allocatable::map(:,:)
  logical,parameter::riku=.true.,umi=.false.
  integer,allocatable::rcdist(:,:)
  character*3000::string
  integer::i,j,k,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
        if(string(j:j)=='.') then
           map(j,i)=umi
        else
           map(j,i)=riku
        end if
     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).eqv.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).eqv.umi)) then
              rcdist(i,j)=k
              exit
           else if(ANY(map(i-k,j-k:j+k).eqv.umi)) then
              rcdist(i,j)=k
              exit
           else if(ANY(map(i-k+1:i+k-1,j+k).eqv.umi)) then
              rcdist(i,j)=k
              exit
           else if(ANY(map(i-k+1:i+k-1,j-k).eqv.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).eqv.riku) then
           max_cdist=MAX(max_cdist, rcdist(i,j))
        end if
     end do
  end do
  print '(i0)',max_cdist
end program