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::io::stdin;

fn main() {
    let mut is = String::new();
    stdin().read_line(&mut is).ok();
    let mut itr = is.split_whitespace().map(|e| e.parse().unwrap());
    let mut x: i64 = itr.next().unwrap();
    let mut n: i64 = itr.next().unwrap();
    let mut is = String::new();
    stdin().read_line(&mut is).ok();
    let mut t = vec![true; 102];
    let mut p = is
        .split_whitespace()
        .map(|e| e.parse().unwrap())
        .collect::<Vec<usize>>();
    for i in p {
        t[i] = false;
    }

    let mut ans = x;
    let mut d = 0;
    loop {
        if x < d {
            ans = -1;
            break;
        }

        let index = (x - d) as usize;
        if t[index] {
            ans = index as i64;
            break;
        }

        let index = (x + d) as usize;
        if t[index] {
            ans = index as i64;
            break;
        }

        d += 1;
    }

    println!("{}", ans);
}