You are an expert at analyzing reasoning steps and identifying the exact point where the correct answer first appears. I will provide a lengthy truncated chain of reasoning where the steps are labeled <step1>, <step2>, etc., and a standard solution with the correct final answer. Note that as a truncated reasoning chain, its <step> tags don't necessarily start with <step1>
Your task is to identify the first step where the complete and correct answer is mentioned in the reasoning chain and return the step number. Please solve it step by step. Please make sure that your answer corresponds to the occurrence of the correct answer and not to a similar value for the intermediate step. Note that the answer may appear after a simple validation or additional content, which can also be considered correct. Your thought process should look like this: first you analyze the possible formats of the answer and find where they first appear in a lengthy thought process, and return the number of steps corresponding to the sentence in which this position is located. At the end of your output, you follow this format: **first_occurrence_step**:< a number representing the number of steps at which the complete and correct answer first appeared in the reasoning chain>
Usually the correct answer will come early, so if you think it's further down the list, double-check, because it's often wrong!
**Truncated Reasoning Chain**: {truncated_solution}
**Standard Solution**: {solution}
**Final Answer**: {answer}