Program to implement interfaces in c#

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication33
{
interface g
{

void add();
}
interface demo :g
{
void sub();
}
class P :demo

{
public void add()
{
Console.WriteLine ("hello");
}
public void sub()
{
Console.WriteLine("sub");
}

}
class d:g
{
public void add()
{
Console.WriteLine("niit");
}
}
class c
{
static void Main(string[] args)
{
P p1 = new P();
p1.add();
d d1 = new d();
d1.add();

}
}
}