using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    public static int FindMissingNumber(int[] A) {

        // write your code in C# 6.0 with .NET 4.5 (Mono)

        var distinct = A.Distinct().OrderBy(a=>a).ToArray();

        var count = distinct.Length;

        var first = distinct[0];

        var last = distinct[count - 1];

        if(first > 1){

            return 1;

        }

        var least = 1;

        for(int i = first; i <= last; i++){

            var index = Array.IndexOf(distinct, i);

            if(index == -1 && i > 0){

                least = i;

                break;

            }

            else if(i > 0){

                least = i + 1;

            }

        }

        return least;

    }

}