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;
#define fo(i,n) for(int i=0;i<n;i++)
#define tr(it, a) for(auto it = a.begin(); it != a.end(); it++)
int main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    int x,n, cc=-1;cin >>x >> n;
    int arr[n];
    fo(i,n){
        cin >> arr[i];
    }
    sort(arr, arr+n);
    fo(i,n){
        if(arr[i]==x){
            cc =i;
        }
    }
    if(cc==-1){
        cout << x;
        return 0;
    }
    int min1 =x-arr[0]+1,min2 =arr[n-1]-x+1, k=1;
    int c = arr[cc];
    for(int i = cc-1; i >=0;--i){
        if(arr[i]!=c-k){
            min1 = k;
            break;
        }
        ++k;
    }
    k =1;
    for(int i = cc+1; i <n;++i){
        if(arr[i]!=c+k){
            min2 = k;
            break;
        }
        ++k;
    }
    if(min2<min1){
        cout << x + min2;
    }
    else{
        cout << x-min1;
    }
  
}