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;
int main(){
  ios_base::sync_with_stdio(false);cin.tie(0);
  int X;
  int N;
  int a = 0;
  int b = 0;
  set<int> s;
  cin>>X;
  cin>>N;
  for(int i = 0;i < N;i++){
    cin>>a;
    s.insert(a);
    //cout<<"A"<<a<<'\n';
  }
  for(int i = 0;i < 100;i++){
    if(s.find(X - i) == s.end()){
      b = X - i;
      break;
    }
    if(s.find(X + i) == s.end()){
      b = X + i;
      break;
    }    
  }
  cout<<b<<'\n';
  // for(int i = 0;i < N;i++){
  //   cin>>a;
  //   s.insert(a);
  //   //cout<<"A"<<a<<'\n';
  // }
  // for(int i = 0;i < 100;i++){
  //   //cout<<X - i<<' ';
  //   //cout<<X + i<<'\n';
  //   if(s.find(X - i) == s.end()){
  //     cout<<X - i<<'\n';
  //     //cout<<"B"<<'\n';
  //     //cout<<"B"<<X - i<<'\n';
  //     break;
  //   }
  //   if(s.find(X + i) == s.end()){
  //     cout<<X - i<<'\n';
  //     //cout<<"A"<<'\n';
  //     //cout<<"C"<<X + i<<'\n';
  //     break;
  //   }
  // }
}