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 C++ (GCC 9.2.1) (judge verdict: Wrong Answer)

#include<bits/stdc++.h>
#include<numeric>
#include<cassert>
//#include <boost/multiprecision/cpp_int.hpp>
#define ll long long int
#define CON 100010
const long long mod=1e9+7;
const int INF=1001001001;
const int inf=100000;
//const ll inf=1e9+7;
//const ll ful=1e18;
using namespace std;
//namespace mp = boost::multiprecision;
int main() 
{
	int x,n;
	cin>>x>>n;
	vector<int> p(n);
	for(int i=0;i<n;i++)
	{
		cin>>p[i];
	}
	//答え
	int ans=inf;
	//直前の最小値
	int pre=inf;
	bool flag=true;
	for(int i=0;i<100;i++)
	{
		flag=true;
		for(int j=0;j<n;j++)
		{
			if(i==p[j]) flag=false;
		}
		if(flag)
		{
			if(pre==abs(x-i)&&ans==i)
			{
				ans=min(ans,i);
			}
			else if(pre>abs(x-i))
			{
				ans=i;
				pre=abs(x-i);
			}
			
		}
	}
	if(n==0) cout<<x<<endl;
	else cout<<ans<<endl;
	return 0;
}