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 Go (1.14.1) (judge verdict: Wrong Answer)

package main

import (
	"fmt"
	"sort"
)

type K struct {
	v, dif int
}

func main() {
	var X, N int
	fmt.Scan(&X, &N)
	if N == 0 {
		fmt.Println(X)
		return
	}
	P := make(map[int]bool)
	for i := 0; i < N; i++ {
		var V int
		fmt.Scan(&V)
		P[V] = true
	}
	KS := []K{}
	for i := -100; i <= 100; i++ { //なんかi=1じゃないらしい（なんで？？？？？
		if !P[i] {
			KS = append(KS, K{v: i, dif: abs(X - i)})
		}
	}
	sort.Slice(KS, func(i, j int) bool {
		if KS[i].dif < KS[j].dif {
			return true
		} else if KS[i].dif > KS[j].dif {
			return false
		} else {
			return KS[i].v < KS[j].v
		}
	})
	if len(KS) > 0 {
		if P[KS[0].v] {
			panic("あわわわわわ")
		} else {
			fmt.Println(KS[0].v)
		}
	} else {
		fmt.Println(0) // なんかXじゃないらしい（なんで？？？？？？？
	}
}

func abs(x int) int {
	if x < 0 {
		x *= -1
	}
	return x
}