===== ISTEM =====
Solve the following programming task.

TASK: Median Finder on a Data Stream

Write a 'MedianFinder' class that accepts numbers from a data stream and computes the running median with O(log n) insertion and O(1) lookup. It must have 'add_num(num)' and 'find_median()' methods.

STARTER CODE (python):
class MedianFinder:
    def __init__(self):
        pass
    def add_num(self, num: int) -> None:
        pass
    def find_median(self) -> float:
        pass


RULES:
- Keep the function name and signature EXACTLY as given.
- Return working code only. No explanations.
- Put the code in a single ``` block.
- Try to solve it first. If you genuinely cannot, write only this single
  line instead of producing faulty code: CANNOT_SOLVE

===== HAM YANIT =====
```python
import heapq

class MedianFinder:
    def __init__(self):
        # max_heap stores the smaller half (using negative values for max-heap behavior)
        self.small = []
        # min_heap stores the larger half
        self.large = []

    def add_num(self, num: int) -> None:
        if len(self.small) == len(self.large):
            heapq.heappush(self.large, -heapq.heappushpop(self.small, -num))
        else:
            heapq.heappush(self.small, -heapq.heappushpop(self.large, num))

    def find_median(self) -> float:
        if len(self.small) == len(self.large):
            return (-self.small[0] + self.large[0]) / 2.0
        else:
            return float(self.large[0])
```