using System;

namespace quizlunedi
{
    class MainClass
    {
        static bool SumExistsUtil(int[] data, int sum, int major_index, int minor_index, bool left)
        {

            while (major_index != minor_index) {

                Console.WriteLine("Confronted values/indexes: "
                                  + major_index + "/" + data[major_index]
                                  + " "
                                  + minor_index + "/" + data[minor_index]);

                int curr_sum = data[major_index] + data[minor_index];

                if (curr_sum == sum)
                    return true;
                else if (left && curr_sum < sum)
                    break;
                else if (!left && curr_sum > sum)
                    break;

                if (left)
                    minor_index--;
                else
                    minor_index++;
            }

            if (major_index != minor_index)
                return SumExistsUtil(data, sum, minor_index,
                                     left ? major_index + 1 : major_index - 1, !left);
            else
                return false;
        }

        static bool SumExists(int[] data, int sum, int data_len)
        {
            return SumExistsUtil(data, sum, 0, data_len-1, true);
        }

        public static void Main (string[] args)
        {
            int[] data = { -20, -19, -1, 0, 1, 4, 7, 8, 9, 10 };

            if (SumExists(data, 80, 10))
                Console.WriteLine ("Sum exists!");
            else
                Console.WriteLine ("Sum don't exists!");
        }
    }
}