------
## 最终结论
```python
def compute_Last_Digit(a, b):
    from math import factorial
    
    result = factorial(b) // factorial(a)
    return result % 10

# Test cases
assert compute_Last_Digit(2,4) == 2
assert compute_Last_Digit(6,8) == 6
assert compute_Last_Digit(1,2) == 2
```