using System;

using System.Collections;

​

public class Program

{

    Hashtable table=new Hashtable();

    public void Triplet(int[] arr,int sum)

    {

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

        {

            table.Add(arr[i],i);

        }

        int count=0;

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

        {

            int j=i+1;

            int k=arr.Length-1;

            while(j<k)

            {

                if(arr[i]+arr[j]+arr[k]>=sum)

                {

                    k--;    

                }

                else

                {

                    count=count+(k-j);

                    j++;

                }

            }

        }

        Console.WriteLine(count);

    }

    public static void Main()

    {

        int[] arr=new int[]{-2, 0, 1, 3};

        int sum=2;

        Program p = new Program();

        p.Triplet(arr,sum);

    }

}