ViewControllerスタックから最上位レベルを削除

if([delete_navigation.visibleViewController isKindOfClass:[TopicViewController class]] && [topicNotification.topic.id isEqualToString:self.otherTopicID]){// 
           
            TopicViewController *controller=(TopicViewController *)delete_navigation.visibleViewController;
            controller.topicNotification=topicNotification;
            controller.topicId=topicNotification.topic.id;
            [controller refreshTopic];
        }else{
            TopicViewController *controller= [[TopicViewController alloc] initWithNibName:@"TopicViewController" bundle:nil];
            controller.topicNotification=topicNotification;
             controller.topicId=topicNotification.topic.id;
            
            if([delete_navigation.topViewController isKindOfClass:[TopicViewController class]]){
                
                NSMutableArray *navigationArray = [[NSMutableArray alloc] initWithArray: delete_navigation.viewControllers];
                
                // [navigationArray removeAllObjects];    // This is just for remove all view controller from navigation stack.
                [navigationArray removeLastObject];  // You can pass your index here
                delete_navigation.viewControllers = navigationArray;
            }
            
            [delete_navigation pushViewController:controller animated:YES];
            
        }