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: Accepted)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define rep(i, n) for(int i = 0; i < (int)(n); ++i)
#define rrep(i, n) for(int i = (int)(n); i>=0; --i)
struct fast_ios { fast_ios(){cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20);} } fast_ios_;

int main()
{
    int X, N;
    cin >> X >> N;
    map<int, bool> mp;
    rep(i, N)
    {
        int p;
        cin >> p;
        mp[p] = true;
    }

    auto it = mp.find(X);
    if(it==mp.end())
    {
        cout << X << endl;
        return 0;
    }
    else
    {
        rep(sa, 100)
        {
            if(mp.find(X-sa)==mp.end())
            {
                cout << X-sa << endl;
                return 0;
            }
            if(mp.find(X+sa)==mp.end())
            {
                cout << X+sa << endl;
                return 0;
            }
        }
    }
    
    return 0;
}