Write a function that takes a positive integer n, sums all the cubed values from 1 to n, and returns that sum.
Assume that the input n will always be a positive integer.
Examples:
```python
sum_cubes(2)
> 9 
# sum of the cubes of 1 and 2 is 1 + 8
```
def sum_cubes(n):
    return (n*(n+1)//2)**2
def sum_cubes(n):
    return (n*(n+1)//2)**2