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)

// -*- coding:utf-8-unix -*-

use num::Float;
use proconio::input;
use std::cmp::Ordering;
use std::collections::VecDeque;
use std::collections::{BTreeSet, HashSet};
use std::io::*;
use std::str::FromStr;
// ABC086C - Traveling
// https://atcoder.jp/contests/abs/fasks/arc089_a

fn switch<T>(flag: bool, t: T, f: T) -> T {
    if flag {
        t
    } else {
        f
    }
}

#[allow(dead_code)]
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}
#[allow(dead_code)]
fn read_string() -> Vec<char> {
    read::<String>().chars().collect()
}
#[allow(dead_code)]
fn read_vector<T: FromStr>(number: usize) -> Vec<T> {
    (0..number).map(|_| read()).collect()
}

fn main() {
    let (x, n): (i32, usize) = (read(), read());
    let ps: Vec<i32> = read_vector(n);

    let value: i32 = (0..101)
        .into_iter()
        .filter(|&y| !ps.contains(&y))
        .min_by(|a: &i32, b: &i32| {
            let a2 = (a - x) * (a - x);
            let b2 = (b - x) * (b - x);
            if a2 == b2 {
                a.cmp(b)
            } else if a2 < b2 {
                Ordering::Less
            } else {
                Ordering::Greater
            }
        })
        .unwrap();

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