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>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);++i)
#define FOR(i,n,j) for(int i=(j);i<(n);++i)
#define rrep(i,n) for(int i=(n);i>=0;--i)
#define ssort(n) sort((n).begin(),(n).end())
using ll=long long;
using ld=long double;
typedef pair<int,int> P;
#define Yes cout << "Yes" << endl
#define No cout << "No" << endl
#define YES cout << "YES" << endl
#define NO cout << "NO" << endl
#define INF 10101010

int main()
{
    int x;
    int n;
    cin >> x >> n;
    vector<int> p(n);
    rep(i,n)cin >> p[i];
    ssort(p);
    int min=INF;
    int min_val=INF;
    vector<int> val(101);
    rep(i,101)val[i]=0;
    rep(i,n)val[p[i]]++;
    int dist=INF;
    for(int i=x;i>-1;--i){
        if(val[i]==0){
            min=i;
            dist=x-i;
            break;
        }
    }
    if(x<100){
        for(int j=x+1;j<=102;++j){
            if(val[j]==0){
                
                if(j-x<dist){
                    min=j;
                    dist=j-x;
                    break;
                }
            }
        }
    }
    
    
    cout << min << endl;
}