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: Runtime Error)

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int main(){
  int X,N;
  cin >> X >> N;
  if(N==0){
    cout << X << endl;
    return 0;
  }
  int tmp=0;
  vector<int> P(N);
  for(int i=0; i<N; i++){
    cin >> tmp;
    P.at(i)=tmp;
  }
  sort(P.begin(), P.end());

  vector<int> P_non;
  bool flag = true;
  for(int i=1; i<=100; i++){
    for(int j=0; j<N; j++){
      if(i == P.at(j)) flag = false;
    }
    if(flag) P_non.push_back(i);
    flag=true;
  }

  int diff=1000;
  int num=1000;
  for(unsigned int i=0; i<P_non.size(); i++){
    if(abs(P_non.at(i)-X) < diff){
      diff = abs(P_non.at(i)-X);
      num = i;
    } 
  } 
  cout << P_non.at(num) << endl;
  return 0;
}