PickingNums

   public static int PickingNumbers(List<int> a)
    {
        int length = 0;
        int temp = 0;
        int firstNumberOfSeq = -1;
        a.Sort();

        for (int i = 1; i < a.Count; ++i)
        {
            int difference = a[i] - a[i - 1];

            if (firstNumberOfSeq == -1 && difference <= 1 && difference >= 0)
            {
                firstNumberOfSeq = a[i - 1];
            }

            if (a[i] - firstNumberOfSeq < 2)
            {
                temp++;
            }
            else
            {
                temp = 0;
                firstNumberOfSeq = -1;
            }

            if (temp > length)
            {
                length = temp;
            }
        }

        return length;
    }