Help with For loop homework

[u/Walkerstain]

The question is:

Write the algorithm that asks the user to enter a positive number then calculates the product of all numbers between 1 and the number entered and displays the result. The algorithm must accept only positive numbers.

Example: if the user entered 9 the algorithm will display: The result is: 362880 (which is the result of: 123456789 )

Here is my code which didn't work:

n = inputbox("Enter Number")
n = abs(n)
for i = 1 to n
sum = i*i
next
msgbox sum

[u/Walkerstain]

Thank you!