class Yukicoder
  attr_accessor :field, :width, :height
  DX = [1, 0, -1, 0]
  DY = [0, 1, 0, -1]

  def initialize
    @width, @height = gets.chomp.split(' ').map(&:to_i)
    @field = []

    height.times do |y|
      @field << gets.chomp.split('')
    end

    id = 0

    height.times do |y|
      width.times do |x|
        if field[y][x] == '.'
          bfs(y, x, id)
          id += 1
        end
      end
    end

    min_dist = Float::INFINITY

    height.times do |y|
      width.times do |x|
        if field[y][x] == '0'
          min_dist = [min_dist, calc_dist(y, x)].min
        end
      end
    end

    puts min_dist
  end

  def calc_dist(y, x)
    coords = [[y,x,0]]
    check_list = Hash.new(false)

    while coords.any?
      y, x, dist = coords.shift

      return dist - 1 if field[y][x] == '1'
      next if check_list[y * width + x]
      check_list[y * width + x] = true

      4.times do |i|
        ny = y + DY[i]
        nx = x + DX[i]

        if is_wall?(ny, nx) && field[ny][nx] != '0'
          coords << [ny, nx, dist + 1]
        end
      end
    end

    Float::INFINITY
  end

  def is_wall?(y, x)
    0 <= y && y < height && 0 <= x && x < width
  end

  def bfs(y, x, id)
    coords = [[y,x]]
    check_list = Hash.new(false)

    while coords.any?
      y, x = coords.shift

      next if check_list[y * width + x]
      check_list[y * width + x] = true

      field[y][x] = id.to_s

      4.times do |i|
        ny = y + DY[i]
        nx = x + DX[i]

        if is_wall?(ny, nx) && field[ny][nx] == '.'
          coords << [ny, nx]
        end
      end
    end
  end
end

Yukicoder.new