using System;

​

public class Program

{

    public static void Main()

    {

        int[] A = {1, 3, 6, 4, 1, 2};

        int counter = 1;

        int solution = 0;

        for (int p = 0; p <= A.Length - 2; p++)

        {

            for (int i = 0; i <= A.Length - 2; i++)

            {

                if (A[i] > A[i + 1])

                {

                    int t = A[i + 1];

                    A[i + 1] = A[i];

                    A[i] = t;

                }

            }

        }

​

        for (int i = 0; i < A.Length; i++)

        {

            if (counter == A[i])

            {

                counter++;

            }

            else

            {

                solution = counter;

            }

        }

        Console.WriteLine(solution);

    }

}