UCBINTC - Good
You are given a sequence A consisting of N integers (not to be confused with the sequence from a previous
task). We will call the ith sequence element good if it equals the sum of some three elements in positions
strictly smaller than i (an element can be used more than once in the sum). How many good elements
does the sequence contain?
The first line of input contains the positive integer N (1 ≤ N ≤ 5000), the length of the se-
quence A. The second line of input contains N space separated integers representing the sequence
A (−100000 ≤ Ai ≤ 100000).
The first and only line of output must contain the number of good elements in the sequence.
Input: 2 1 3 Output: 1
Input: 6 1 2 3 5 7 10 Output: 4
Input: 3 -1 2 0 Output: 1