Problems with Cancel Button and UIActionSheet

How do I determine if the cancel button was pressed on a UIActionSheet?

My UIActionSheet is set up like this:

-(IBAction)fileButtonPressed
{
    UIActionSheet *mymenu = [[UIActionSheet alloc] 
                             initWithTitle:@"Select Folder" 
                             delegate:self 
                             cancelButtonTitle:@"Cancel" 
                             destructiveButtonTitle:nil 
                             otherButtonTitles:nil];

    for (i=0; i<3; i++) 
    { 
        [mymenu addButtonWithTitle:@"Button Name"]; 
    }

    [mymenu showInView:self.view];

}

The problem that I have is that I cannot differentiate between the cancel button and the first button selected.

-(void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex
{  
    NSString *option = [actionSheet buttonTitleAtIndex:buttonIndex];

    //buttonIndex == 0 if the cancel button is pressed or 
    //if the first item is pressed.
}

Is there a better way of setting this up?