N = gets.to_i
H = Array.new(N + 1){ Array.new(N + 1) }
(1 .. N).each do |i|
  gets.split.each.with_index(1) do |h,j|
    H[i][j] = h
  end
end
ANS = (1 .. N).select do |j|
  (1 .. N).all?{|i| i == j || H[i][j] == 'nyanpass' }
end
puts ANS.size == 1 ? ANS[0] : -1