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 JavaScript (Node.js 12.16.1) (judge verdict: Accepted)

"use strict";

const main = arg => {
    const inputList = arg.trim().split("\n");
    // 回答を記述
    const X = parseInt(inputList[0].split(" ")[0]);
    const N = parseInt(inputList[0].split(" ")[1]);
    if (N == 0) {
        console.log(X)
    } else {
        const PList = inputList[1].split(" ").map(ele => parseInt(ele))

        const hundred = [...Array(100).keys()].map(i => ++i)
        hundred.unshift(0);

        const notExistPList = hundred.filter(ele => PList.indexOf(ele) == -1)

        const result = notExistPList.reduce((acc, cur) => {
            const accDif = Math.abs(X - acc);
            const curDif = Math.abs(X - cur);
            if (accDif == curDif) {
                return Math.min(acc, cur);
            } else if (accDif > curDif) {
                return cur;
            } else {
                return acc;
            }
        }, 101);

        if (Math.abs(X - result) >= Math.abs(X - (-1))) {
            console.log(-1)
        } else {
            console.log(result)
        }
    }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));