Help!! So I need some help with programming (python)

Here's my code:
import itertools
def sumOfLargest(a1, a2, a3):
a1 = [int(x) for x in a1.split()]
a2 = [int(x) for x in a2.split()]
a3 = [int(x) for x in a3.split()]
print(sum(map(max, itertools. zip_longest(a1, a2, a3, fillvalue=0
if __name__ == '__main__':

a1 = input()

a2 = input()

a3 = input()

But I get this error:

Traceback (most recent call last):
File "Solution. py", line 34, in
result = sumOfLargest(a1, a2, a3)
File "Solution. py", line 24, in sumOfLargest
print(sum(map(max, itertools. zip_longest((a1,a2,a3), fillvalue=0
TypeError: unsupported operand type(s) for +: 'int' and 'list'

Does anyone know why? Or how to fix it?