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: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
    int x, n; cin >> x >> n;
    unordered_set<int> s;
    for (int i = 0; i < 200; ++i) {
        s.insert(i);
    }
    for (int i = 0; i < n; ++i) {
        int p; cin >> p;
        s.erase(p);
    }
    int ans = 300;
    int m = INT_MAX;
    vector<int> v(s.begin(), s.end());
    sort(v.begin(), v.end(), greater<int>());
    for (const auto &e: s) {
        if (abs(e - x) <= m) {
            ans = e;
            m = abs(e - x);
            continue;
        }
    }
    cout << ans << endl;
    return 0;
}