@n = gets.to_i
@a = @n.times.map{gets.chomp}
@m = [*0...@n].combination(2).to_a
@ml = @m.length
@mi = 100
def check(i)
  w = [0]*@n
  (0...@ml).each do |j|
    c, d = @m[j]
    if (1<<j) & i > 0
      w[c] += 1
      return if @a[c][d] == 'x'
    else
      w[d] += 1
      return if @a[c][d] == 'o'
    end
  end
  r = 1
  w = w.uniq
  w[1..-1].each{|j| r += 1 if j > w[0]}
  @mi = r if r < @mi
end
(0...(1<<@ml)).each{|i| check(i)}
p @mi