title: Print substrings 3 characters long in between certain other substrings
body: <p>I'm trying to print substrings of genes given a genome through user input. (User inputs AATTATGTTTAGTAGTTAGAAA) I need to print characters in sets of three after the first time ATG is printed, and end printing sets of three once the genome reaches TAG, TGA, TAA, or ATG (a second time).</p>
  <p>In the example given above of the genome AATTATGTTTAGTAGTTAGAAA, I'd need to print TTT, then on a separate line AGT, then AGT again on another separate line, and then stop once I reach TAG.</p>