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: Runtime Error)

use std::io;

fn main() {
    let stdin = io::stdin();
    let (X,N) = {
	let mut buf = String::new();
	stdin.read_line(&mut buf).unwrap();
	let mut split = buf.split_ascii_whitespace();
	(
	    split.next().unwrap().parse::<u16>().unwrap(),
	    split.next().unwrap().parse::<usize>().unwrap()
	)
    };

    if N == 0 {
	println!("{}",X);
	std::process::exit(-1);
    }
    
    let seq: Vec::<u16> = {
	let mut buf = String::new();
	stdin.read_line(&mut buf).unwrap();
	buf.retain(|c| c !='\n');
	buf.split_ascii_whitespace().map(|s| s.parse::<u16>().unwrap()).collect()
    };

    println!("{}",solve(X, seq.as_ref()));
}

fn solve(x : u16, list : &[u16]) -> u16{
    let mut foo = Vec::from(list);
    if !list.contains(&x){
	x
    }else{
	foo.sort();
	
	let last_num = foo[foo.len()-1];
	let first_num = foo[0];

	if x <= first_num || x > (last_num + 1){
	    x - 1
	}else{
	    let mut index = 0;
	    loop{
		if !foo.contains(&(x - index)){
		    return x - index;
		}else if !foo.contains(&(x + index)){
		    return x + index;
		}
		index += 1;
	    }
	}
    }
}