Definition: In this task, you're given the title of a story consisting of five sentences, numbered 1 through 5. Your job is to determine which two sentences need to be swapped sentences in order to make a story that makes complete sense and is befittingly titled. Indicate your answer using the numbers of the two sentences in order, such as '34' or '25'. The first digit refers to the sentence which should come first in the story.
Input: Title: The Breakup. Sentence 1: Katie finally decided she'd had enough. Sentence 2: David and Katie had been having problems. Sentence 3: She told him to move his stuff out. Sentence 4: He got mad and broke her favorite vase. Sentence 5: Katie knew she'd made the right decision.
Output:
21