ModAdd

import fileinput

with fileinput.input(['z']) as input:
    a = list(input.readline().rstrip())
    b = list(input.readline().rstrip())
    res = []
    a.reverse()
    b.reverse()
    for i in range(max(len(a), len(b))):
        try:
            a_i = int(a[i])
        except IndexError:
            res += b[i:]
            break
        try:
            b_i = int(b[i])
        except IndexError:
            res += a[i:]
            break
        res.append(str((a_i + b_i) % 10))
    res.reverse()
    print(int(''.join(res)))

Test 1

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 2

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 3

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 4

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 5

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 6

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 7

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 8

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 9

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...

Test 10

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 4, in <module>
    a = lis...