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)

macro_rules! get_tuple {
    ($($t:ty),*) => {
        {
            let mut line: String = String::new();
            std::io::stdin().read_line(&mut line).unwrap();
            let mut iter = line.split_whitespace();
            (
                $(iter.next().unwrap().parse::<$t>().unwrap(),)*
            )
        }
    };

    ($($t:ty),*; $n:expr) => {
        (0..$n).map(|_|
            get_tuple!($($t),*)
        ).collect::<Vec<_>>()
    };
}

macro_rules! get_vec {
    ($t:ty) => {
        {
            let mut line: String = String::new();
            std::io::stdin().read_line(&mut line).unwrap();
            line.split_whitespace()
                .map(|t| t.parse::<$t>().unwrap())
                .collect::<Vec<_>>()
        }
    };
    ($t:ty; $n:expr) => {
        (0..$n).map(|_| get_vec!($t)).collect::<Vec<_>>()
    };
}

fn main() {
    let (x, n) = get_tuple!(isize, isize);
    let v_p = get_vec!(isize);

    if v_p.len() == 0{
        println!("{}", x);
        return
    }

    let diff: Vec<_> = v_p.iter().map(|e| e - x).collect();

    let short_vec = generate_short_vec(100_usize);

    for i in short_vec {
        if diff.iter().all(|&e| e != i) {
            println!("{}", x + i);
            break
        }
    }

}

fn generate_short_vec(n: usize) -> Vec<isize> {
    let mut v = vec![0];

    for i in 1..=n {
        v.push(-(i as isize));
        v.push(i as isize);
    }

    v
}