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)

#!/usr/bin/env ruby
# require 'pry'

# dpテンプレ
# 最小化
# dp = Hash.new{ Float::INFINITY }
# dp[i] = [dp[i], dp[i-1] + hoge].min
# dp[0] = 0
# 最大化
# dp = Hash.new{ 0 }
# dp[i] = [dp[i], dp[i-1] + hoge].max
# dp[0] = 0

x,n = gets.split(' ').map(&:to_i)
P = gets.split(' ').map(&:to_i)
if n == 0
  puts x
  exit
end

0.upto(100) do |num|
  a = x-num
  b = x+num
  if P.include?(a) && P.include?(b)
    next
  elsif P.include?(a)
    puts b
    exit
  else
    puts a
    exit
  end
end