Description

Given $N$ rectangles whose geometric centers are at the origin of the Cartesian coordinate system. Paint these $N$ rectangles, and find the total painted area.

Input Format

The first line contains an integer $N$.

The next $N$ lines each contain two even integers $X, Y$, representing the rectangle’s width and height (corresponding to the horizontal length and the vertical length, respectively).

Output Format

Output the total painted area.

3
8 2
4 4
2 6

28

5
2 10
4 4
2 2
8 8
6 6

68

Hint

[Sample 1 Illustration]

[Constraints]

For $40\%$ of the testdata, all input integers are less than $3333$.

For $50\%$ of the testdata, there are no rectangles that contain another.

For $100\%$ of the testdata, $1 \le N \le 10^6$, $2 \le X, Y \le 10^7$.

[Hints and Notes]

This problem is translated from COCI 2016-2017 CONTEST #5 T3 Unija.

The score of this problem follows the original COCI settings, with a full score of $100$.

Translated by ChatGPT 5