import scala.collection.mutable.{Set=>MSet}

object Main {
  val Consonants = "nbmgr"
  val Vowels = "iaaeuu"

  def solve(usedNames: MSet[String]):String = {
    for (conps <- Consonants.permutations; vowps <- Vowels.permutations) {
      val cons = conps.toString
      val vows = vowps.toString
      val vowslast = vows.last.toString
      var tenchars = ""
      for ((c, v) <- cons zip vows) {
        tenchars += c
        tenchars += v
      }
      for (i <- 0 to 10) {
        val candidate = tenchars.patch(i, vowslast, 0)
        if (!usedNames(candidate)) {
          return candidate
        }
      }
    }
    return "NO"
  }

  def main(args: Array[String]): Unit = {
    val scanner = new java.util.Scanner(System.in)
    val n = scanner.nextInt()
    var usedNames = MSet() : MSet[String]
    for (_ <- 0 until n) {
      usedNames(scanner.next()) = true
    }
    val answer = solve(usedNames)
    println(answer)
  }
}