1945. Sum of Digits of String After Convert
## 思路
第1輪把字元都轉成數字再加總digit
第2~k輪就digit加總
## Code
```python
class Solution:
def getLucky(self, s: str, k: int) -> int:
res = 0
for ch in s:
pos = ord(ch) - ord('a') + 1
res += pos // 10 + pos % 10
for _ in range(1, k):
curr = 0
while res:
res, digit = divmod(res, 10)
curr += digit
res = curr
return res
```