Sum of Two Others

Problem Background

Special for beginners, ^_^

Problem Description

Given a sequence of positive integers, count how many of them are equal to the sum of two other numbers in the sequence. For example, for the sequence $1\ 2\ 3\ 4$, the answer is $2$, because $3 = 2 + 1$ and $4 = 1 + 3$.

Input Format

Two lines in total. The first line is the number $n$ ($1 \le n \le 100$) of elements in the sequence. The second line contains the $n$ positive integers (each not greater than $10000$) forming the sequence, separated by a single space.

Output Format

One integer: the number of elements in the sequence that equal the sum of two other elements.

Sample Input

4
1 2 3 4

Sample Output

2

Constraints

Time limit: 1s, memory limit: 1024KiB for each test case.