Given a premise, an initial context, an original ending, and a counterfactual context, the task is to generate a new story ending aligned with the counterfactual context and as close to the original ending as possible. Each instance consists of a five-sentence story. The premise is the first sentence of a story, and the second sentence, which is the initial context, provides more information about the story's context and the story's general plot. The original ending is the last three sentences of the story. Also, a counterfactual context is a slight modification to the initial context. You should write a new story ending that edits the original story ending as little as possible to regain coherence with the counterfactual context. To sum up, you should write the last three sentences of a story based on the premise(first sentence) and the counterfactual context(second sentence) of the story.
Q: Premise: Zack's son wanted a bike for his birthday. 
 Initial Context: But he knew he couldn't afford one. 
 Original Ending: While Zack waited at a bus stop one day, he saw a bike with no lock. So he grabbed it and took in on the bus with him. When Zack's son got the bike for his birthday, he was ecstatic. 
 Counterfactual Context: Zack's sister had promised to help him with the costs.
A: 
While Zack waited at a bus stop one day, he saw a bike with no lock. So he grabbed it and took in on the bus with him. When Zack's son got the bike for his birthday, he was ecstatic, but he felt guilty for stealing the other bike. 