'else' Function help

• 
  
  conventinal = ("1337")
  
  heavy = ("2448")
  
  textutils.slowWrite ("ENTER LAUNCH CODE FOR THE HEAVY OR CONVENTINAL MISSILES:")
  input = read()
  
  if  input == conventinal then
  rs.setOutput ("left", true)
  
  elseif input == heavy then
  rs.setOutput ("right", true)
  
  if input == else then 
  textutils.slowPrint("CODE INVALID!!! SHUTTING DOWN")
  os.shutdown
  
  end
  
  sleep(1)
  textutils.slowWrite ("Missiles are FIRING! Look in the sky!!!!")
  sleep(2) 
  textutils.slowWrite ("Action Completed")
  sleep(3)
  os.shutdown()
  

conventinal = "1337"
heavy = "2448"
textutils.slowWrite ("ENTER LAUNCH CODE FOR THE HEAVY OR CONVENTINAL MISSILES:")
input = read()
if  input == conventinal then
rs.setOutput ("left", true)
elseif input == heavy then
rs.setOutput ("right", true)
else --You don't need to put if input == else, just else will work. That's where your error was.
textutils.slowPrint("CODE INVALID!!! SHUTTING DOWN")
os.shutdown() --You forgot () at the end there.
end
sleep(1)
textutils.slowWrite ("Missiles are FIRING! Look in the sky!!!!")
sleep(2)
textutils.slowWrite ("Action Completed")
sleep(3)
os.shutdown()