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: Runtime Error)

package main

import (
	"fmt"
	"sort"
)

func main() {
	var x, n int
	fmt.Scan(&x, &n)

	if n == 0 {
		fmt.Println(x)
		return
	}

	var p []int
	for i := 0; i < n; i++ {
		var a int
		fmt.Scan(&a)
		p = append(p, a)
	}
	sort.Ints(p)

	point := sliceIndex(p, x)

	for i := 0; ; i++ {
		flag := sliceIndex(p, p[point]-i)
		if flag == -1 {
			fmt.Println(x - i)
			return
		}
		flag = sliceIndex(p, p[point]+i)
		if flag == -1 {
			fmt.Println(x + i)
			return
		}
	}
}

func sliceIndex(a []int, b int) int {
	for i, e := range a {
		if e == b {
			return i
		}
	}
	return -1
}