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.io.*;
import java.math.*;
public class Main{

	public static void main(String args[]){
		FastReader sc = new FastReader();
		StringBuilder sb=new StringBuilder();
		int t,i,n,x;
		t=1;
		while(t-->0){
            x=sc.nextInt();
            n=sc.nextInt();
            int a[]=new int[n];
            HashSet<Integer> set=new HashSet<>();
            for(i=0;i<n;i++){
                a[i]=sc.nextInt();
                set.add(a[i]);
            }
            int temp=x;
            int min=Integer.MAX_VALUE;
            int num=x;
            int count=0;
            while(temp>=0){
                int val=x-temp;
                if(!set.contains(temp)&&val<min){
                    min=val;
                    num=temp;
                    break;
                }
                temp--;
                count++;
            }
            temp=x;
            while(temp<=x+count){
                int val=temp-x;
                if(!set.contains(temp) && val<min){
                    min=val;
                    num=temp;
                }
                temp++;
            }
            sb.append(num).append('\n');
		}
		sb.deleteCharAt(sb.length()-1);
		out.println(sb);
	}

	static PrintWriter out;
	static class FastReader{
		BufferedReader br;
		StringTokenizer st;
		public FastReader(){
			br=new BufferedReader(new InputStreamReader(System.in));
			out=new PrintWriter(System.out,true);
		}
		String next(){
			while(st==null || !st.hasMoreElements()){
				try{
					st= new StringTokenizer(br.readLine());
				}
				catch (IOException e){
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}
		int nextInt(){
			return Integer.parseInt(next());
		}
		long nextLong(){
			return Long.parseLong(next());
		}
		double nextDouble(){
			return Double.parseDouble(next());
		}
		String nextLine(){
			String str = "";
			try{
				str=br.readLine();
			}
			catch(IOException e){
				e.printStackTrace();
			}
			return str;
		}
	}

	public static boolean isPrime(int n) {
		if(n<2) return false;
		for(int i=2;i<=(int)Math.sqrt(n);i++) {
			if(n%i==0) return false;
		}
		return true;
	}

	public static void print(int a[],int l,int r){
		int i;
		for(i=l;i<=r;i++)
			out.print(a[i]+" ");
		out.println();
	}

	public static long fastexpo(long x, long y, long p){
		long res=1;
		while(y > 0){
			if((y & 1)==1)
				res= ((res%p)*(x%p))%p;
			y= y >> 1;			
			x = ((x%p)*(x%p))%p;
		}
		return res;
	}

	public static boolean[] sieve (int n) {
		boolean primes[]=new boolean[n+1];
		Arrays.fill(primes,true);
		primes[0]=primes[1]=false;
		for(int i=2;i*i<=n;i++){
			if(primes[i]){
				for(int j=i*i;j<=n;j+=i)
					primes[j]=false;
			}
		}
		return primes;
	}

	public static long gcd(long a,long b){
        return (BigInteger.valueOf(a).gcd(BigInteger.valueOf(b))).longValue();
    }

    public static void merge(long a[],int l,int m,int r){
        int n1,n2,i,j,k;
        n1=m-l+1;
        n2=r-m;

        long L[]=new long[n1];
        long R[]=new long[n2];

        for(i=0;i<n1;i++)
            L[i]=a[l+i];
        for(j=0;j<n2;j++)
            R[j]=a[m+1+j];

        i=0;j=0;

        k=l;
        while(i<n1&&j<n2){
            if(L[i]<=R[j]){
                a[k]=L[i];
                i++;
            }
            else{
                a[k]=R[j];
                j++;
            }
            k++;
        }

        while(i<n1){
            a[k]=L[i];
            i++;
            k++;
        }
        while(j<n2){
            a[k]=R[j];
            j++;
            k++;
        }
    }
    public static void sort(long a[],int l,int r){
        int m;
        if(l<r){
            m=(l+r)/2;
            sort(a,l,m);
            sort(a,m+1,r);
            merge(a,l,m,r);
        }
    }
}