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 1.8.0) (judge verdict: Accepted)

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.*;

public class Main {
    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    public static void main(String args[]) throws Exception {
        String[] tokens = br.readLine().split(" ");
        int x = Integer.parseInt(tokens[0]);
        int n = Integer.parseInt(tokens[1]);
        Set<Integer> set = new HashSet<>();
        if(n>0){
            tokens = br.readLine().split(" ");
            for(int i=0;i<n;i++){
                set.add(Integer.parseInt(tokens[i]));
            }
        }
        int ans = x;
        for(int diff=0;diff<=Integer.MAX_VALUE;diff++){
            int left = x-diff;
            int right = x+diff;
            if(!set.contains(left)){
                ans = left;
                break;
            }
            if(!set.contains(right)){
                ans = right;
                break;
            }
        }
        System.out.println(ans);
    }




    private static class Pair{
        int first,second;

        public Pair(int first,int second){
            this.first = first;
            this.second = second;
        }

        public int hashCode(){
            return Objects.hash(first,second);
        }

        public boolean equals(Object obj){
            if(obj!=null || !(obj instanceof  Pair))
                return false;
            Pair pair = (Pair)obj;
            return pair.first == first && pair.second == second;
        }
    }




}