class ToDoList: def init(self): self.tasks = []

def add_task(self, task):
    self.tasks.append({'task': task, 'completed': False})
    print(f"Added task: {task}")

def mark_completed(self, task_number):
    if 0 <= task_number < len(self.tasks):
        self.tasks[task_number]['completed'] = True
        print(f"Marked task {task_number} as completed.")
    else:
        print("Invalid task number.")

def remove_completed_tasks(self):
    self.tasks = [task for task in self.tasks if not task['completed']]
    print("Removed all completed tasks.")

def view_tasks(self):
    if not self.tasks:
        print("No tasks available.")
    else:
        for i, task in enumerate(self.tasks):
            status = "Completed" if task['completed'] else "Not Completed"
            print(f"{i}: {task['task']} - {status}")

def main(): todo_list = ToDoList()

while True:
    print("\nTo-Do List Application")
    print("1. Add Task")
    print("2. Mark Task as Completed")
    print("3. Remove Completed Tasks")
    print("4. View Tasks")
    print("5. Exit")

    choice = input("Enter your choice: ")

    if choice == '1':
        task = input("Enter the task: ")
        todo_list.add_task(task)
    elif choice == '2':
        task_number = int(input("Enter the task number to mark as completed: "))
        todo_list.mark_completed(task_number)
    elif choice == '3':
        todo_list.remove_completed_tasks()
    elif choice == '4':
        todo_list.view_tasks()
    elif choice == '5':
        print("Exiting the application.")
        break
    else:
        print("Invalid choice. Please try again.")

if name == "main": main()