------
## 最终结论
```python
def average_Odd(n):
    if n % 2 == 0:
        raise ValueError("Input must be an odd number.")
    
    odd_numbers = [i for i in range(1, n + 1, 2)]
    return sum(odd_numbers) // len(odd_numbers)

# Test cases
assert average_Odd(9) == 5
assert average_Odd(5) == 3
assert average_Odd(11) == 6
```