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>
#define rep(i,n) for (int i=0;i<(n);++i)
using namespace std;
using ll = long long;
using P= pair<int,int>;

int main() {
    
    int X,N;
    int answer=0;
    bool match=false;
    cin>>X>>N;
    
    vector<int> d(102);//forbidden list
    rep(i,N){
      int p;
      cin>>p;
      d[p]=1;
    }
    P ans(99999,-1);
    for(int i=0; i<=101;++i)
    {
      if(d[i]==1)continue;
      int dif=abs(X-i);
      ans = min(ans,P(dif,i));
    }
    cout<<ans.second<<endl;
    return 0;
}