Given a number N, find the sum of all its factors.

Example 1:

Input: N = 30
Output: 72
Explanation: Factors sum 1 + 2 + 3 + 5 
+ 6 + 10 + 15 + 30 = 72

Example 2:

Input: N = 15
Output: 24
Explanation: Factors sum 1 + 3 + 5 
+ 15 = 24

Your Task:  
You don't need to read input or print anything. Your task is to complete the function factorSum() which takes N as input and returns the sum.

Expected Time Complexity: O(sqrt N)
Expected Auxiliary Space: O(1)

Constraints:
1 ≤ N ≤ 10⁹