There are several mobile operating systems that power smartphones and tablets.
Some of the most common ones include:
1. Android - A popular open-source OS, developed by Google, used on a wide variety of smartphones.
2. iOS - Developed by Apple for use on its iPhone, iPad, and iPod devices.
3. Windows Phone - A now-discontinued mobile OS developed by Microsoft, previously used on Nokia and other devices.
4. HarmonyOS - A new operating system developed by Huawei for its smartphones and IoT devices.
On the day of her examination, Riya sharpened her pencil from both ends as shown below. 
The diameter of the cylindrical and conical part of the pencil is 4.2 mm. If the height of each conical part is 2.8 mm and the length of the entire pencil is 105.6 mm, find the total surface area of the pencil.