import scala.io.StdIn.readLine
import scala.collection.mutable.PriorityQueue
import scala.annotation.tailrec
import scala.util.control.Breaks

object Main {
  // def insert(s : String, c : Char, n : Int) : String = {
  //   val (head,tail) = s.splitAt(n)
  //   head + c + tail
  // }
  def solve(s : String) : Option[String] = {
    val n = s.length
    val b = new Breaks
    def check(s : String,c : Char) : Boolean = {
      val n = s.length
      (0 until s.length).forall((i) => {
                                  val j = n - i - 1
                                  s(i) == c || s(j) == c || s(i) == s(j)
                                })
    }
    if(check(s,'?')){
      Some(s.take(n/2) + s(n/2) + s.drop(n/2))
    }else{
      var ans : Option[String] = None
      b.breakable {
        for(i <- 0 until n){
          val j = n - i - 1
          if(s(i) != s(j)){
            val checking = Vector((s.take(i) + "?" + s.drop(i)),
                                  (s.take(j+1) + "?" + s.drop(j+1)))
            println(checking)
            checking.foreach((i) => if(check(i,'?')){
                               val r = i.indexOf('?')
                               ans = Some(i.updated(r,i(n-r)))
                             })
            b.break
          }
        }
      }
      ans
    }
  }
  def main(args : Array[String]) : Unit = {
    val s = readLine
    val ret = solve(s) match {
        case Some(j) => j
        case None    => "NA"
      }
    println(ret)
  }
}