error compiling Mono in debian etch

[Brad Brock <brad_brock@yahoo.com>]

I want to use stdlib in Mono.
This is my source code 

using Mono;
using System;
using System.IO;

class yoursourcefileclass
{
    public static void Main(String[] Args)
    {
        Console.WriteLine(" Random Number: {0}", Mono.Unix.rand());
    }
}


I've some trouble when I compile my source code, this is the error message : 
test.cs(9,44): error CS0234: The type or namespace name `Unix' does not exist in the namespace `Mono'. Are you missing an assembly reference?
Compilation failed: 1 error(s), 0 warnings

Do I miss some package to install? How should I fix it?

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