lib C
  fun strtoll(s : UInt8*, p : UInt8**, b : Int32) : Int64
end

class String
  def to_i64
    C.strtoll(self, nil, 10)
  end
end

vowel, cons = "iaaeuu", "nbmgr"
size = vowel.size + cons.size

strings = [] of String
(0...6).each { |vowel_pos|
  f = [0, 1] * 5
  f.insert({0, vowel_pos * 2 - 1}.max, 1)

  vowel.chars.each_permutation { |v|
    cons.chars.each_permutation { |c|
      v_i, c_i = -1, -1
      strings << (0...size).map { |i|
        if f[i] == 0
          c_i += 1
          cons[c_i]
        else
          v_i += 1
          vowel[v_i]
        end
      }.join
    }
  }
}
strings.uniq!

n = read_line.to_i
s = (1..n).map { read_line }.sort

ans = strings.find { |str|
  s.bsearch { |i| i >= str } != str
}

puts ans ? ans : "NO"