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 Rust (1.42.0) (judge verdict: Accepted)

use proconio::{input, fastout};
use std::collections::HashSet;

macro_rules! echo {
  ($val:expr) => {
    println!("{}", $val);
  }
}

#[fastout]
fn main() {
  input!{
    x: i32,
    n: usize,
    ps: [i32; n]
  };

  let mut ans = 201;
  let mut set = HashSet::new();
  for p in ps {
    set.insert(p);
  }
  for i in 0..102 {
    if set.contains(&i) {
      continue;
    }
    if (ans - x).abs() > (i - x).abs() {
      ans = i;
    }
  }
  echo!(ans);
}