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 Python (3.8.2) (judge verdict: Accepted)

import sys

def saiki(l,r,lst):
  if (l - 1) not in lst:
      return (l - 1)
  
  if (r + 1) not in lst:
      return (r + 1)
  
  return saiki(l - 1, r + 1, lst)

def main():
  # Xはもっとも近い整数，Nは与えられるP
  X,N = map(int, input().split())

  arr = list(map(int, input().split()))

  if N == 0:
    print(X)
    sys.exit()

  if X not in arr:
    print(X)
    sys.exit()

  print(saiki(X,X,arr))

if __name__ == '__main__':
    main()