# 全探索・・・

def fill(map)
  ret = []

  xys = []
  xys << map.map.with_index{|row,y| x = row.index("."); [x, y]}
                .find{|x,y| x && y}
  while xy = xys.shift do
    x, y = xy
    if map[y][x] == "." then
      map[y][x] = " "
      ret << [x, y]
      xys << [x + 1, y]
      xys << [x - 1, y]
      xys << [x, y + 1]
      xys << [x, y - 1]
    end
  end

  return ret
end

gets
map = $stdin.read.lines.map{|l| l.chomp.chars}
as = fill(map)
bs = fill(map)

mds = []
as.each do |xa, ya|
  bs.each do |xb, yb|
    mds << (xa - xb).abs + (ya - yb).abs
  end
end

puts mds.min - 1