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)

#![allow(unused_imports)]
#![allow(dead_code)]
use datastructure::*;
use grapth::*;
use input_scanner::*;
use math::*;
use string_algorithm::*;
use util::*;

use std::cmp;
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, LinkedList, VecDeque};

fn main() {
    let mut scan = Scanner::new();
    let x: i32 = scan.next();
    let n: usize = scan.next();
    let p: Vec<i32> = scan.next_vec(n);

    let mut ans = 100000;
    for i in -200..200 {
        if p.iter().any(|a| *a == i) {
            continue;
        }
        if (x - i).abs() < (x - ans).abs() {
           ans = i;
        }
    }

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

mod datastructure {}
mod grapth {}
mod math {}
mod string_algorithm {}
mod util {}
mod input_scanner {
    pub struct Scanner {
        bytes: Vec<u8>,
        begin: usize,
        end: usize,
    }

    impl Scanner {
        pub fn new() -> Self {
            use std::io::Read;
            let mut buffer: Vec<u8> = Vec::new();
            std::io::stdin().read_to_end(&mut buffer).unwrap();
            let end = (0..buffer.len())
                .find(|i| buffer[*i].is_ascii_whitespace())
                .unwrap_or(buffer.len());
            Scanner {
                bytes: buffer,
                begin: 0,
                end: end,
            }
        }
        pub fn next<T: std::str::FromStr>(&mut self) -> T {
            let s: &str =
                unsafe { std::str::from_utf8_unchecked(&self.bytes[self.begin..self.end]) };
            let ret: T = s.parse::<T>().ok().expect("Parse error.");
            self.skip();
            ret
        }
        pub fn next_vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
            (0..n).map(|_| self.next()).collect()
        }
        pub fn next_word(&mut self) -> Vec<u8> {
            let r = Vec::from(&self.bytes[self.begin..self.end]);
            self.skip();
            r
        }
        fn skip(&mut self) {
            self.begin = (self.end..self.bytes.len())
                .find(|i| !self.bytes[*i].is_ascii_whitespace())
                .unwrap_or(self.bytes.len());
            self.end = (self.begin..self.bytes.len())
                .find(|i| self.bytes[*i].is_ascii_whitespace())
                .unwrap_or(self.bytes.len());
        }
    }
}