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 std::collections::HashSet;

fn main(){
  let mut buf = String::new();
  std::io::stdin().read_line(&mut buf).expect("failed to read");
  let mut it = buf.split_whitespace();
  let x: u32 = it.next().unwrap().parse().unwrap();
  let n: u32 = it.next().unwrap().parse().unwrap();

  if n == 0 {
    println!("{}", x);
  } else {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).expect("failed to read");
    let hs: HashSet<u32> = buf.split_whitespace().map(|e| e.parse().unwrap()).collect();

    let mut i: u32 = 0;

    loop {
      if ! hs.contains(&(x - i)) {
        println!("{}", x - i);
        break;
      } else if ! hs.contains(&(x + i)) {
        println!("{}", x + i);
        break;
      } else {
        i += 1;
      }
    }
  }
}