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: Wrong Answer)

fn get_line() -> String {
    let mut line = String::new();
    std::io::stdin().read_line(&mut line).unwrap();
    line.trim().to_string()
}

fn main() {
    let (x, n) = {
        let ab = get_line()
            .split_whitespace()
            .map(|e| e.parse().unwrap())
            .collect::<Vec<isize>>();
        (ab[0], ab[1])
    };

    let mut ps = get_line()
        .split_whitespace()
        .map(|e| e.parse().unwrap())
        .collect::<Vec<isize>>();
    ps.sort();

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

    let (max, min) = (ps.iter().max().unwrap(), ps.iter().min().unwrap());
    let v: Vec<isize> = (*min..=*max).filter(|x| !ps.contains(x)).collect();

    let mut minimum = 100000000;
    let mut current = *min;

    for i in &v {
        if (x - i).abs() < minimum {
            minimum = x - i;
            current = *i;
        }
    }

    if current == *min {
        println!("{}", min - 1);
    } else if current - x > x {
        println!("{}", min - 1);
    } else {
        println!("{}", current);
    }
}