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::{
   fastout, input,
   marker::{Bytes, Chars, Isize1, Usize1},
};

use std::collections::HashSet;

fn main() {
   input! {
      x:isize,n:usize,
      p:[isize;n]
   }
   let s = p.iter().map(|x| *x).collect::<HashSet<_>>();

   if n == 0 {
      println!("{}", x);
      return;
   }
   let mut a = 999;
   let mut b = -999;
   for i in x..200 {
      if !s.contains(&i) {
         a = i;
         break;
      }
   }
   for i in (-100..=x).rev() {
      if !s.contains(&i) {
         b = i;
         break;
      }
   }
   if (a - x).abs() < (b - x).abs() {
      println!("{}", a);
   } else {
      println!("{}", b);
   }
}