Get input

Steps

1. Understand the problem.
1. We need to get the value from the input device.
2. It may change on each execution.
3. We also need to load the value for PI as it will be used in a later step.
   
2. Design a solution.
1. Ask the user for a radius value.
2. Get input from user and store in the container, radius.
3. Copy the value from the literal, 3.14 and write it in the container, PI.
3. Test the solution.