using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        int n = 2;

        int[] arr = new int[] {2,3,4,5,6,7};

        int[] combination = new int[n];

        CombinationUtil(arr,combination,0,2,0);

    }

    private static void CombinationUtil(int[] arr,int[] combination,int index,int n,int i)

    {

        Console.WriteLine(string.Format("i {0}: Index {1}",i,index));

        if ( index == n )

        {

            for(int k=0;k<n;k++)

            {

                Console.Write(combination[k] + ",");

            }

            Console.WriteLine();

            return;

        }

        if ( i >= arr.Length )

            return;

        combination[index] = arr[i];

        CombinationUtil(arr,combination,index+1,n,i+1);

        CombinationUtil(arr,combination,index,n,i+1);

    }

}