Lesson 4- Bai 1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Bai1
{
    class Program
    {

        static void Main(string[] args)
        {
            int n;
            int[] a;
            bool[] res;
            n = int.Parse(Console.ReadLine());
            a = new int[n];

            string[] temp = Console.ReadLine().Split();
            for (int i = 0; i < n; i++)
            {
                a[i] = int.Parse(temp[i]);
            }
            int maxTemp = findMax(a);

            res = new bool[maxTemp + 1];

            for (int i = 0; i < n; i++)
            {
                res[a[i]] = true;
            }

            for (int i = 1; i < res.Length; i++)
            {
                if (!res[i]) {
                    Console.WriteLine(i);
                    break;
                }
            }
        }

        static int findMax(int[] a)
        {
            int max = a[0];

            for (int i = 1; i < a.Length; i++)
            {
                if (a[i] > max) max = a[i];
            }
            return max;
        }

    }
}