An integer X (1 ≤ X ≤ 10^18).
An integer Y (X ≤ Y ≤ 10^18).

### Example Input:

```
3 20
```

### Function Signature:
Write a function f(X, Y) that takes in the input.
def f(X: int, Y: int):
    ''' 
    X: an integer 
    Y: an integer
    '''