title: how to if and elif this code for print "impossible"(python)
body: <p>This is my code -</p>
  
  <pre><code>"""NumDays"""
  from datetime import date
  def cal_date(day1, month1, day2, month2):
      """process"""
      d0 = date(2017, month1, day1)
      d1 = date(2017, month2, day2)
      delta = abs(d1 - d0)
      print(delta.days)
  cal_date(int(input()), int(input()), int(input()), int(input()))
  
  </code></pre>
  
  <p>if day out of range for month i want to print "impossible" but i don't have any idea.</p>