using System;

using System.Collections.Generic;

​

class Program

{

    static bool HasPairWithSum(int[] numbers, int k)

    {

        HashSet<int> seenNumbers = new HashSet<int>();

​

        foreach (int num in numbers)

        {

            int complement = k - num;

            if (seenNumbers.Contains(complement))

            {

                return true;

            }

            seenNumbers.Add(num);

        }

​

        return false;

    }

​

    static void Main()

    {

        int[] numbers = { 10, 2, 6, 13 };

        int k = 23;

​

        bool result = HasPairWithSum(numbers, k);

        Console.WriteLine(result ? "Yes, there is a pair." : "No, there isn't a pair.");

    }

}