Minimize all the program at a time

Suppose you are doing something alone and you don't wanna let people see what you are doing. Suddenly someone appears and you want to minimize all the program quickly. It will be too late if you try to minimize all the programs by using your mouse pointer. But if you use Windows menu +D shortcut, you can easily minimize all the program. Apply the same shortcut again to maximize all the program. This is a very useful shortcut you must use.