------
## 最终结论
```python
def set_left_most_unset_bit(n):
    # Find the position of the leftmost unset bit
    position = 0
    while n & (1 << position):
        position += 1
    
    # Set that bit
    n |= (1 << position)
    
    return n

# Test cases
assert set_left_most_unset_bit(10) == 14
assert set_left_most_unset_bit(12) == 14
assert set_left_most_unset_bit(15) == 15
```