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)

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

use proconio::input;

// ABC086C - Traveling
// https://atcoder.jp/contests/abs/fasks/arc089_a

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

    p.sort();
    match p.binary_search(&x) {
        Ok(n) => {
            let mut lower = p[n];
            let mut i = 1;
            loop {
                if !p.contains(&(p[n] - i)) {
                    lower = p[n] - i;
                    break;
                }
                i += 1;
            }

            let mut greater = p[n];
            let mut i = 1;
            loop {
                if !p.contains(&(p[n] + i)) {
                    greater = p[n] + i;
                    break;
                }
                i += 1;
            }

            if (lower - x).abs() > (greater - x).abs() {
                println!("{}", greater);
            } else {
                println!("{}", lower);
            }
        },
        Err(n) => {
            println!("{}", x);
        }
    }
}