y = int(1.999999999999999) # fifteen decimal points
print(y)
1       # output is 1

y = int(1.9999999999999999) # sixteen decimal points
print(y)
2       # output is 2
It shows 1 when we type fifteen decimal whereas when we add sixteen decimal points the output becomes 2.

Please study the docs first:

https://docs.python.org/3/tutorial/floatingpoint.html

That will give you the background to understand why `int()` has nothing to do with this.

>>> 1.9999999999999999
2.0

That is, `int()` was passed 2.0 to begin with, because the binary float closest to the decimal value 1.9999999999999999 is in fact 2.0.

If you can't live with that, use the `decimal` module instead:

>>> import decimal
>>> int(decimal.Decimal("1.9999999999999999"))
1