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.*;

public class Main {
    public static void main(String[] args) throws Exception {
        
        Scanner scanner = new Scanner(System.in);
        int X = scanner.nextInt();
        int N = scanner.nextInt();
        HashSet<Integer> set1 = new HashSet<Integer>();
        HashSet<Integer> set2 = new HashSet<Integer>();
        int sa = 1000;
        int num = 0;
        
        for(int i=0; i<N; i++){
            int n = scanner.nextInt();
            set1.add(n);
        }
        
        for(int i=0; i<100; i++){
            if(!set1.contains(i+1)){
                set2.add(i+1);
            }
        }
        
        for(int i: set2){
            if(Math.abs(i-X)<sa){
                sa = Math.abs(i-X);
                num = i;
            }
        }
        
        if(X<=50){
            if(X<=Math.abs(num-X)){
                System.out.println(0);
            }else{
                System.out.println(num);
            }
        }else{
            if(101-X<Math.abs(num-X)){
                System.out.println(101);
            }else{
                System.out.println(num);
            }
        }
        
    }
}