input: Write a python function to validate IPv4 addresses.
  assert check_valid_ip("192.168.1.1") == True
  assert check_valid_ip("255.255.255.255") == True
  assert check_valid_ip("256.256.256.256") == False
  assert check_valid_ip("192.168.1") == False
output: def check_valid_ip(ip):
      parts = ip.split('.')
      if len(parts) != 4:
          return False
      for part in parts:
          if not part.isdigit():
              return False
          num = int(part)
          if num < 0 or num > 255:
              return False
      return True