Simon Says

Simon asks you to perform operations on a list of numbers that only he tells you. You should ignore all other instructions given. Create a function which evaluates a list of commands (written in plain English) if the command begins with Simon says. Return the result as an integer.

Examples

simon_says([
  "Simon says add 4",
  "Simon says add 6",
  "Then add 5"
]) ➞ 10

simon_says([
  "Susan says add 10",
  "Simon says add 3",
  "Simon says multiply by 8"
]) ➞ 24

simon_says([
  "Firstly, add 4",
  "Simeon says subtract 100"
]) ➞ 0

Notes

• If no instructions are given by Simon, return 0.
• For the sake of simplicity, there will be no command for dividing.