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.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int X = scanner.nextInt();
        int N = scanner.nextInt();

        ArrayList<Integer> smaller = new ArrayList<>();
        ArrayList<Integer> bigger = new ArrayList<>();

        for (int i = 0; i < N; i++) {
            int temp = scanner.nextInt();
            if (temp < X) {
                smaller.add(temp);
            } else {
                bigger.add(temp);
            }
        }

        scanner.close();

        Collections.sort(smaller);
        Collections.reverse(smaller);
        Collections.sort(bigger);

        int small = -1;
        int big = -1;
        for (int i = 0; i < smaller.size(); i++) {
            if (X - 1 - i != smaller.get(i)) {
                small = X - 1 - i;
                break;
            }
        }

        for (int i = 0; i < bigger.size(); i++) {
            if (X + i != bigger.get(i)) {
                big = X + i;
                break;
            }
        }

        if (bigger.size() > 0 && smaller.size() > 0) {
            if (small == -1) {
                small = smaller.get(smaller.size() - 1) - 1;
            }
            if (big == -1) {
                big = bigger.get(bigger.size() - 1) + 1;
            }

            if (X - small < big - X) {
                System.out.println(small);
            } else if (X - small > big - X) {
                System.out.println(big);
            } else {
                System.out.println(small);
            }
        } else if (bigger.size() == 0) {
            System.out.println(X);
        } else if (smaller.size() == 0) {
            if (bigger.contains(X)) {
                System.out.println(X - 1);
            } else {
                System.out.println(X);
            }
        }

    }
}