Nested Loop to Generate Triangle

[Babbare]

I need the triangle to be in reverse. The assignment requires a nested loop to generate a triangle with the user input of how many lines.

Currently, I get answers such as:
OOOO
OOO
OO
O

When I actually need it to be like this:


I just need to get it flipped-over on the other side.

base_size = int(input("How many lines? "))
columns = base_size

for row in range (base_size) :
   for columns in range (columns) :
       print('O', end='')
   print()