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@John Joe - You could have let the OP try debugging the code before giving the answer.
Can you explain to the OP how you found the problem?

It's important to know how to debug code and find the...

Try debugging the code to see if you can find the problem.

Add some print statements that show the values of the variables as they are used and changed.
For example print the values passed to...

Ok, that's a start.
Now please add comments to the output saying what is wrong with it.
For example:
line 1
line 3 <<<<< this should say line 2
line 3

Can you copy and paste here the contents of the console that shows what you are talking about?
Add some comments describing the problem.