subroutine create_map(map,H,W)
  implicit none
  logical,parameter::riku=.true.,umi=.false.
  character*3000::string
  integer(kind=4)::H,W,i,j
  logical,allocatable::map(:,:)

  read *,H,W

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

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

end subroutine create_map

program main
  implicit none
  interface
     subroutine create_map(map,H,W)
       logical,allocatable::map(:,:)
       integer::H,W
     end subroutine create_map
  end interface
  integer(kind=4)::H,W
  logical,allocatable::map(:,:)
  logical,parameter::riku=.true.,umi=.false.
  integer,allocatable::dist_h(:),dist_w(:)
  integer::i,j,k,l,max_dist=1,dist

  call create_map(map,H,W)

  do dist=MIN(H/2,W/2),0,-1
     do i=dist,W-dist+1
        do j=dist,H-dist+1
           if(map(i,j).eqv.riku) then
              if(ALL(ALL(map(i-dist:i+dist,j-dist:j+dist),1))) then
                 print '(i0)', dist+1
                 return
              end if
           end if
        end do
     end do

  end do

end program main