Code Performance Profiler

Profile this code for performance issues:

[PASTE CODE]

1. Identify the top 3 performance bottlenecks. For each, explain WHY it's slow (Big-O, IO blocking, repeated allocations, etc.).
2. Propose a specific optimization for each.
3. Estimate the speedup (rough order of magnitude).
4. Identify the lowest-hanging fruit - the optimization with best ROI (largest speedup per line of code change).
5. Provide the optimized code only for the top recommendation. Don't refactor everything at once.

If the code is already efficient, say so honestly.