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.
Q: Title: Mom. Sentence 1: He knew she always wanted to go to Paris with his dad. Sentence 2: John's mom was dying. Sentence 3: So John booked a flight to Paris for his dad and mom. Sentence 4: Payed for their hotel and their other expenses. Sentence 5: John was glad to hear from his dad that she was having a good time.
A:
21