using System;

using System.Collections;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        int [] numbers =  {1, 2, 0};

        Console.WriteLine(numeroFaltante(numbers));

    }

    public static int numeroFaltante(int [] numbers){

        List<int> numerosOrdenados = new List<int>();

        numerosOrdenados.AddRange(numbers); 

        numerosOrdenados.Sort();

        int menor = 1;

        foreach(int number in numerosOrdenados){

            if(number>0){

                if(number<menor){

                    menor = number;

                }else if(menor==number){

                    menor+=1;

                }

            }

        }

        return menor;

    }

}