------
## 最终结论
```python
def sum_digits_twoparts(n):
    str_n = str(n)
    max_sum = 0
    
    # Iterate over possible split points
    for i in range(1, len(str_n)):
        part1 = int(str_n[:i])
        part2 = int(str_n[i:])
        digit_sum = sum(int(d) for d in str(part1)) + sum(int(d) for d in str(part2))
        
        if digit_sum > max_sum:
            max_sum = digit_sum
            
    return max_sum

# Test cases
assert sum_digits_twoparts(35) == 17
assert sum_digits_twoparts(7) == 7
assert sum_digits_twoparts(100) == 19
```