Given an array of integers, form three sub arrays s1, s2, s3 such that
sum(s2) <= sum(s1)+sum(s3).
Return the number of such subarrays that can be formed

Eg)
Input
[2,3,5,7]
Output
3
Explanation
subarrays are

• s1 = [2], s2 = [3], s3 = [5,7]
• s1 = [2,3], s2 = [5], s3 = [7]
• s1 = [2], s2 = [3,5], s3 = [7]