import scala.io.StdIn.readLine
import scala.collection.mutable.PriorityQueue
import scala.annotation.tailrec

// PriorityQueue[Long]()(scala.math.Ordering.Long.reverse)
package net.pushl {
  package number {
    // Prime  (Prime.scala)
    // Number (Number.scala)
  }
  package string {
    // RollingHash (RollingHash.scala)
  }
  object EnRich {
    implicit class AString(val self : String) extends AnyVal {
      def splitToIntArray = self.split(" ").map(_.toInt)
    }
  }
}

import net.pushl.EnRich._
object Main {
  def main(args : Array[String]) : Unit = {
    val c = readLine().toInt
    val n = readLine().toInt
    val a = readLine().splitToIntArray

    val v = Array.fill[Option[Int]](c+1)(None)
    v(0) = Some(0)
    for(i <- a){
      for(k <- i to c){
        (v(k),v(k-i)) match {
          case (Some(a),Some(b)) => v(k) = Some(a min (b+1))
          case (None   ,Some(b)) => v(k) = Some(b+1)
          case (_      ,None   ) => {}
        }
      }
    }
    val out = v(c) match {
        case Some(k) => k
        case None    => -1
      }
    println(out)
  }
}