import scala.collection.mutable.ListBuffer

object Main{
  def main(args: Array[String]){
    val input=io.Source.stdin.getLines().mkString("\n");
    println(solve(input).trim());
  }

  def solve(input:String):String={
    val Array(nm, _as) = input.split("\n");
    val Array(n,m) = nm.split(" ").map(_.toInt)
    val as = _as.split(" ").map(_.toInt-1)
    var cards = ListBuffer((1 to n):_*)
    for(a <- as){
      cards = cards.remove(a) +: cards
    }
    cards.head.toString
  }
}