input: Write a python function to retrieve the top n elements from a collection.
  
  assert larg_nnum([10, 20, 50, 70, 90, 20, 50, 40, 60, 80, 100], 2) == [100, 90]
  assert larg_nnum([10, 20, 50, 70, 90, 20, 50, 40, 60, 80, 100], 5) == [100, 90, 80, 70, 60]
  assert larg_nnum([10, 20, 50, 70, 90, 20, 50, 40, 60, 80, 100], 3) == [100, 90, 80]
output: def larg_nnum(collection, n):
      return sorted(collection, reverse=True)[:n]