input: Write a python function to validate international phone numbers using a regular expression.
  assert validate_phone_number("+1-800-867-5309")
  assert not validate_phone_number("1-800-867-5309")
  assert validate_phone_number("+44-20-7123-4567")
  assert not validate_phone_number("+1-800-867-530")
output: def validate_phone_number(phone_number):
      import re
      pattern = re.compile(r'^\+\d{1,3}-\d{1,4}-\d{3,4}-\d{4}$')
      return bool(pattern.match(phone_number))