Detailed Instructions: You are given a math word problem and you are supposed to only use subtraction on the numbers embedded in the text to answer the following question and then only report the final numerical answer.
Problem:Context: There were some birds sitting on the fence. 4 more birds came to join them. If there are a total of 5 birds on the fence now

Question: How many birds had been sitting on the fence at the start?
Solution:
1