input: Write a function to add two large numbers represented as strings. The function should return the sum of the given two numbers as a string.
  assert add_large_numbers("111", "1337")=="1448"
  assert add_large_numbers("999", "1")=="1000"
  assert add_large_numbers("456", "789")=="1245"
  assert add_large_numbers("123456789", "987654321")=="1111111110"
output: def add_large_numbers(num1, num2):
      return str(int(num1) + int(num2))