input: Write a Python function to convert a given positive integer into its Roman numeral representation in lowercase. The integer should be in the range from 1 to 1000.
  assert int_to_lowercase_roman(19) == 'xix'
  assert int_to_lowercase_roman(152) == 'clii'
  assert int_to_lowercase_roman(251) == 'ccli'
  assert int_to_lowercase_roman(426) == 'cdxxvi'
  assert int_to_lowercase_roman(500) == 'd'
  assert int_to_lowercase_roman(1) == 'i'
  assert int_to_lowercase_roman(4) == 'iv'
  assert int_to_lowercase_roman(43) == 'xliii'
  assert int_to_lowercase_roman(90) == 'xc'
  assert int_to_lowercase_roman(94) == 'xciv'
  assert int_to_lowercase_roman(532) == 'dxxxii'
  assert int_to_lowercase_roman(900) == 'cm'
  assert int_to_lowercase_roman(994) == 'cmxciv'
  assert int_to_lowercase_roman(1000) == 'm'
output: def int_to_lowercase_roman(num):
      val = [
          1000, 900, 500, 400,
          100, 90, 50, 40,
          10, 9, 5, 4,
          1
          ]
      syb = [
          'm', 'cm', 'd', 'cd',
          'c', 'xc', 'l', 'xl',
          'x', 'ix', 'v', 'iv',
          'i'
          ]
      roman_num = ''
      for i in range(len(val)):
          count = int(num / val[i])
          roman_num += syb[i] * count
          num -= val[i] * count
      return roman_num