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 proconio::input;
use std::cmp;

fn main() {
    input! {
        x: i32,
        n: usize,
        ps: [i32; n],
    }

    let mut nums = (1..=100).collect::<Vec<_>>();
    nums.retain(|v| !ps.contains(v));

    if nums.is_empty() {
        let ans = if x < (x - 101).abs() { x } else { 101 };
        println!("{}", ans);
        return;
    }

    let mut ans = nums[0];
    for &v in &nums[1..] {
        if (v - x).abs() == (ans - x).abs() {
            ans = cmp::min(ans, v);
        } else if (v - x).abs() < (ans - x).abs() {
            ans = v;
        }
    }

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