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 sz 100002
#define pb push_back
#define ff first
#define ss second
#define ll long long
#define VEC vector<int>v
#define TEST() int test;cin>>test; while(test--)
#define FAST() ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
using namespace std;

//ll int LCM(ll int a,ll int b) { ll int gcd=__gcd(a,b);ll int lcm=a*b/gcd;return lcm;}
//ll int bigmod(ll int b, ll int p, ll int m){if(p==0)return 1;if(p%2!=0) return b%m*fun(b,p-1,m)%m;if(p%2==0){ ll int res=fun(b,p/2,m);return (res%m*res%m)%m;}}
//void seive() { prime[np++]=2;for(i=3; i<=sz; i+=2){if(mark[i]==0){ prime[np++]=i;for(j=i*i; j<=sz; j+=i) mark[j]=1; } }}
//string add(string s1,string s2) {string s;int j=s1.size()-1,c=0,m; for(int i=s2.size()-1; i>=0; i--) {if(j>=0)m=s2[i]-'0'+s1[j]-'0'+c;else m=s2[i]-'0'+c; if(m>9) { s+=m%10+'0';c=m/10; } else {  c=0;s+=m+'0'; }j--; } if(c!=0) {s+=c+'0'; }reverse(s.begin(),s.end());return s;}
//int pos;string mul(int n) {string s;for(int i=0; i<pos; i++) { s+="0"; }pos++;int c=0,m; for(int i=s1.size()-1; i>=0; i--) { m=(s1[i]-'0')*n+c;if(m>9) { s+=m%10+'0';c=m/10;} else { c=0; s+=m+'0';} }while(c!=0) { s+=c%10+'0';c=c/10;}    reverse(s.begin(),s.end());return s;}

int main()
{
    FAST();

     int n,m,a,b,res=1000;
    cin>>m>>n;
    VEC;
    map<int,int>mp;

    if(n==0)
    {
        cout<<m<<endl;
        return 0;
    }
    for(int i=0; i<n; i++)
    {
        cin>>a;
        v.pb(a);
        mp[a]++;
    }

    for(int i=0; i<n; i++)
    {
        a=v[i]-1;
        if(mp[a]==0)
        {

            if(abs(a-m)<res)
            {
                res=abs(a-m);
                b=a;
            }


        }
        a=v[i]+1;
        if(mp[a]==0)
        {
            if(abs(a-m)<res)
            {
                res=abs(a-m);
                b=a;
            }

        }


    }
    cout<<b<<endl;

}