#82 arraycount1

Loading problem...

Preparing the statement, recent submissions, and submit form.

#82 arraycount1 | DOJ

Time limit: 2000 ms
Memory limit: 1024 MB
Checker: CUSTOM
Solve threshold: 100

Statement

A positive integer $N$ and a sequence $A = [A_1, A_2, \cdots, A_{2N}]$ of length $2N$ are given. Find the number of integer pairs $(i, j)$ that satisfy the following conditions.

$1 \leq i \leq N$ .
$1 \leq j \leq N$ .
$A_i + A_j = A_{i + j}$ .

Input

The input is given in the following format.

$N$ $A_1 \ A_2 \ \cdots \ A_{2N}$

Output

Print the answer of the problem on the first line.

Constraints

$1 \leq N \leq 2 \ 000$ .
$1 \leq A_i \leq 1 \ 000 \ 000 \ 000$ ( $1 \leq i \leq 2N$ ).

Subtasks

#	Score	Constraints
1	37	$N \leq 200$ .
2	63	No additional constraints.

Samples

Sample 1

Input

3
1 2 3 7 5 10

Output

Sample 2

Input

4
1 2 3 4 5 6 7 8

Output