input: Write a python function to obtain the highest possible number created from the provided digits.
  assert largest_number([1,2,3],3) == 321
  assert largest_number([4,5,6,1],4) == 6541
  assert largest_number([1,2,3,9],4) == 9321
output: def largest_number(digits, n):
      digits.sort(reverse=True)
      return int(''.join(map(str, digits)))