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 Ruby (2.7.1) (judge verdict: Accepted)

X,N = gets.split.map(&:to_i)  # スペースで区切られた複数の整数
X.freeze
N.freeze
if N == 0 then
  puts X
  exit
end
p = gets.split.map(&:to_i)  # スペースで区切られた複数の整数

p.sort!

#初期化
wkp = 0
wkm = 0
ans = X
#X自身が答えの判定
if p.include?(X) == false then
  puts X
  exit
end

loop do
  #マイナス側判定
  wkm = wkm - 1
  if p.include?(X-(wkm.abs)) == false then
  puts X-(wkm.abs)
  exit
  end
  #プラス側判定
  wkp = wkp + 1
  if p.include?(X+(wkp.abs)) == false then
  puts X+(wkp.abs)
  exit
  end
end