Problem:
Score : 300 points

Problem Statement

Given are an integer X and an integer sequence of length N: p_1, \ldots, p_N.

Among the integers not contained in the sequence p_1, \ldots, p_N (not necessarily positive), find the integer nearest to X, that is, find the integer whose absolute difference with X is the minimum. If there are multiple such integers, report the smallest such integer.

Constraints

1 \leq X \leq 100

0 \leq N \leq 100

1 \leq p_i \leq 100

p_1, \ldots, p_N are all distinct.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

X N
p_1 ... p_N

Output

Print the answer.

Sample Input 1

6 5
4 7 10 6 5

Sample Output 1

8

Among the integers not contained in the sequence 4, 7, 10, 6, 5, the one nearest to 6 is 8.

Sample Input 2

10 5
4 7 10 6 5

Sample Output 2

9

Among the integers not contained in the sequence 4, 7, 10, 6, 5, the ones nearest to 10 are 9 and 11. We should print the smaller one, 9.

Sample Input 3

100 0

Sample Output 3

100

When N = 0, the second line in the input will be empty. Also, as seen here, X itself can be the answer.

Solution in Scala (2.13.1) (judge verdict: Wrong Answer)

import java.util.Scanner

import scala.annotation.tailrec

object Main extends App {
  val sc = new Scanner(System.in)
  val X, N = sc.nextInt
  if (N == 0) {
    println(X)
  } else {
    val seq = (0 until N).foldLeft(Vector.fill(100)(true)) { (acc, _) =>
      val next = sc.nextInt - 1
      acc.updated(next, false)
    }.zipWithIndex
    //    System.err.println(seq)

    @tailrec def loop(n: Int): Int = {
      val smaller = seq.take(X - n).lastOption
      //      System.err.println(s"smaller: $smaller")
      val larger = seq.drop(X - 1 + n).headOption
      //      System.err.println(s"larger: $larger")
      if (smaller.exists(_._1)) smaller.get._2
      else if (larger.exists(_._1)) larger.get._2
      else loop(n + 1)
    }

    val ans = loop(0)
    println(ans + 1)
  }
}