how can i add these 3 records to SortedList

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace SortedListDemo
{
class Sorted_List
{
int id, marks;
string name;
public Sorted_List(int id, string name, int marks)
{
this.id = id;
this.name = name;
this.marks = marks;
}
public override string ToString()
{
return String.Format("id: {0,-5} name: {1,-5} marks : { 2}",id,name,marks);
}
}
class SortedList1
{

static void Main(string[] args)
{
SortedList<Sorted_List, int> sobj = new SortedList<Sorted_List, int>();
Sorted_List s = new Sorted_List(1, "hello", 34);
Sorted_List s1 = new Sorted_List(20, "world", 32);
Sorted_List s2 = new Sorted_List(0, "hai", 98);
//here not adding the records,giving string format exception
sobj.Add(s, 3);
sobj.Add(s1, 0);
sobj.Add(s2, 1);
foreach (KeyValuePair<Sorted_List, int> s4 in sobj)
{
Console.WriteLine(s4);
}
}
}