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)

use std::collections::HashSet;
fn main() {
    let mut init = String::new();
    std::io::stdin().read_line(&mut init).unwrap();
    let x = init
        .split_whitespace()
        .map(|i| i.parse::<i32>().unwrap())
        .nth(0)
        .unwrap();
    let mut input: HashSet<i32> = {
        let mut s = String::new();
        std::io::stdin().read_line(&mut s).unwrap();
        s.split_whitespace()
            .map(|i| i.parse::<i32>().unwrap())
            .collect()
    };
    let mut value = 101;
    let mut count = -1;
    for n in -1..101 {
        if input.contains(&n) {
            continue;
        }
        if (n - x).abs() < value {
            value = (n - x).abs();
            count = n;
        }
    }
    println!("{}", count);
}