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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.*;
import java.lang.Integer; 

public class Main {
  public static void main(String[] args){
    
    int answer = 0; // 返却値
    // 入力
    Scanner sc = new Scanner(System.in);
    int x = sc.nextInt();
    if(!sc.hasNext()){
      System.out.println(answer);
       return;
    }
    int n = sc.nextInt();
    
    // nが0のとき
    if(n == 0){
      answer = x;
      System.out.println(answer);
      return;
    }
    
    // 入力値の読み込み
    Set<Integer> pSet = new HashSet<Integer>();
    while(sc.hasNext()){
      pSet.add(sc.nextInt());
    }
    
    // 数字を検索する
    int a = 0;
    while(true){
      if(!pSet.contains(x - a)){
        answer = x - a;
        break;
      }
      if(!pSet.contains(x + a)){
        answer = x + a;
        break;
      }
      a++;
    }
    // 出力
    System.out.println(answer);
  }
}