iPhone - dismiss multiple ViewControllers

I have a long View Controllers hierarchy;

in the first View Controller I use this code:

SecondViewController *svc = [[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];
[self presentModalViewController:svc animated:YES];    
[svc release];

In the second View Controller I use this code:

ThirdViewController *tvc = [[ThirdViewController alloc] initWithNibName:@"ThirdViewController" bundle:nil];
[self presentModalViewController:tvc animated:YES];    
[tvc release];

and so on.

So there is a moment when I have many View Controllers and I need to come back to the first View Controller. If I come back one step at once, I use in every View Controller this code:

[self dismissModalViewControllerAnimated:YES];

If I want to go back directly from the, say, sixth View Controller to the first one, what I have to do to dismiss all the Controllers at once?

Thanks