Language: Go

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"

	"flag"
	"runtime"
	"runtime/pprof"
)

var magic = 1000000007

var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")
var memprofile = flag.String("memprofile", "", "write mem profile to file")

var N int
var p [200000]int

func find(n int) int {
	for i := 0; i < N; i++ {
		if n == p[i] {
			return 0
		}
	}
	return 1
}

func solve() {
	io := NewIo()
	defer io.Flush()

	X := io.NextInt()
	Logf("%v\n", X)
	N = io.NextInt()
	Logf("%v\n", N)
	for i := 0; i < N; i++ {
		p[i] = io.NextInt()
	}
	Logf("p %v\n", p[0:10])

	for i := 0; i <= 100; i++ {
		if find(X-i) == 1 {
			fmt.Printf("%v\n", X-i)
			os.Exit(0)
		}
		if find(X+i) == 1 {
			fmt.Printf("%v\n", X+i)
			os.Exit(0)
		}
	}

}

func main() {
	flag.Parse()
	if *cpuprofile != "" {
		f, err := os.Create(*cpuprofile)
		if err != nil {
			Logf("%v\n", err)
			os.Exit(1)
		}
		pprof.StartCPUProfile(f)
		defer pprof.StopCPUProfile()
	}

	solve()

	if *memprofile != "" {
		f, err := os.Create(*memprofile)
		if err != nil {
			Logf("could not create memory profile: ", err)
			os.Exit(1)
		}
		defer f.Close()
		runtime.GC()
		if err := pprof.WriteHeapProfile(f); err != nil {
			Logf("could not write memory profile: ", err)
			os.Exit(1)
		}
	}
}

type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buffer []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buffer = append(buffer, line...)
		if !isPrefix {
			break
		}
	}
	return string(buffer)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	r := io.tokens[io.nextToken]
	io.nextToken++
	return r
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) PrintLn(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntLn(a []int) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.PrintLn(b...)
}

func (io *Io) PrintStringLn(a []string) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.PrintLn(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func Logf(format string, a ...interface{}) {
	fmt.Fprintf(os.Stderr, format, a...)
}

func intMin(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func intMax(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func combination(n, m int) int {
	if m > n {
		return 0
	} else if m == n || m == 0 {
		return 1
	} else {
		res := 1
		for i := 0; i < m; i++ {
			res *= (n - i)
		}
		for i := 1; i <= m; i++ {
			res /= i
		}
		return res
	}
}

func lucas(n, m, p int) int {
	ntemp := n
	mtemp := m
	res := 1
	for i := 0; i < 100; i++ {

		nreminder := ntemp % p
		ntemp = ntemp / p
		mreminder := mtemp % p
		mtemp = mtemp / p
		res = res * (combination(nreminder, mreminder) % p)
		if ntemp == 0 {
			break
		}
	}
	return res % p
}

func combMod(n, m, p int) int {
	return lucas(n, m, p)
}

func bfs(start int, nodes map[int][]int, fn func(int)) {
	frontier := []int{start}
	visited := map[int]bool{}

	for 0 < len(frontier) {
		next := []int{}
		for _, node := range frontier {
			visited[node] = true
			fn(node)
			for _, n := range bfsFrontier(node, nodes, visited) {
				next = append(next, n)
			}
		}
		frontier = next
	}
}

func bfsFrontier(node int, nodes map[int][]int, visited map[int]bool) []int {
	next := []int{}
	iter := func(n int) bool { _, ok := visited[n]; return !ok }
	for _, n := range nodes[node] {
		if iter(n) {
			next = append(next, n)
		}
	}
	return next
}

func dfs(node int, nodes map[int][]int, fn func(int)) {
	dfsRecur(node, nodes, map[int]bool{}, fn)
}

func dfsRecur(node int, nodes map[int][]int, v map[int]bool, fn func(int)) {
	v[node] = true
	fn(node)
	for _, n := range nodes[node] {
		if _, ok := v[n]; !ok {
			dfsRecur(n, nodes, v, fn)
		}
	}
}

func dfs2(node int, nodes map[int][]int, fn1, fn2 func(int, int)) {
	dfs2Recur(node, -1, nodes, map[int]bool{}, fn1, fn2)
}

func dfs2Recur(node, parent int, nodes map[int][]int, v map[int]bool, fn1, fn2 func(int, int)) {
	v[node] = true
	if fn1 != nil {
		fn1(node, parent)
	}
	for _, n := range nodes[node] {
		if _, ok := v[n]; !ok {
			dfs2Recur(n, node, nodes, v, fn1, fn2)
		}
	}
	if fn2 != nil {
		fn2(node, parent)
	}
}

type Stack struct {
	top  *Element
	size int
}

type Element struct {
	value interface{}
	next  *Element
}

func (s *Stack) Len() int {
	return s.size
}

func (s *Stack) Push(value interface{}) {
	s.top = &Element{value, s.top}
	s.size++
}

func (s *Stack) Pop() (value interface{}) {
	if s.size > 0 {
		value, s.top = s.top.value, s.top.next
		s.size--
		return
	}
	return nil
}

func powerInt(n, p int) int {
	tmp := 1
	for i := 0; i < n; i++ {
		tmp *= p
	}
	return tmp
}

func findDivisors(n int, a *[]int) {
	if n == 1 {
		return
	}

	sqrt := int(math.Sqrt(float64(n)))
	for i := 2; i <= sqrt; i++ {
		if n%i == 0 {
			*a = append(*a, i)
			*a = append(*a, n/i)
		}
	}
	*a = append(*a, n)
}

func removeDuplicate(a []int) []int {
	m := make(map[int]bool)
	for i := 0; i < len(a); i++ {
		m[a[i]] = true
	}
	res := []int{}
	for i := range m {
		res = append(res, i)
	}
	return res
}

func abs(a int) int {
	if a > 0 {
		return a
	}
	return -a
}

func gcd(a, b int) int {
	for a != 0 {
		a, b = b%a, a
	}
	return b
}

func power2mod(n, mod int) int {
	res, x := 1, 2
	for ; n > 0; n >>= 1 {
		if n&1 == 1 {
			res = res * x % mod
		}
		x = x * x % mod
	}
	return res
}

func power2(n int) int {
	return power2mod(n, magic)
}


Example test case(s):
input: 6 5
4 7 10 6 5

output: 8