How To Get A List Of All The Computers Within A Domain

I have a code to get a list of all the computers within a domain. Now i need to just get the computers which are within a particular OU and not the rest of the machines. so here is my code to get all the machines from a domain, this works perfectly fine:

DirectoryEntry entry = new DirectoryEntry("LDAP://" + selectDomain);
DirectorySearcher mySearcher = new DirectorySearcher(entry);
mySearcher.Filter = ("(objectClass=computer)");
mySearcher.SizeLimit = int.MaxValue;
mySearcher.PageSize = int.MaxValue;
foreach (SearchResult resEnt in mySearcher.FindAll())
{
//"CN=SGSVG007DC"
string ComputerName = resEnt.GetDirectoryEntry().Name;
if (ComputerName.StartsWith("CN="))
ComputerName = ComputerName.Remove(0, "CN=".Length);
compList.Add(ComputerName);
}
mySearcher.Dispose();
entry.Dispose();