input: Write a function to add two large numbers represented as strings.
  assert add_large_numbers("111", "1337")=="1448"
  assert add_large_numbers("999", "1")=="1000"
  assert add_large_numbers("9999", "1")=="10000"
  assert add_large_numbers("123", "456")=="579"
  assert add_large_numbers("0", "0")=="0"
output: def add_large_numbers(num1, num2):
      return str(int(num1) + int(num2))