Problem:
Score : 400 points

Problem Statement

On a two-dimensional plane, there are N red points and N blue points.
The coordinates of the i-th red point are (a_i, b_i), and the coordinates of the i-th blue point are (c_i, d_i).

A red point and a blue point can form a friendly pair when, the x-coordinate of the red point is smaller than that of the blue point, and the y-coordinate of the red point is also smaller than that of the blue point.

At most how many friendly pairs can you form? Note that a point cannot belong to multiple pairs.

Constraints

All input values are integers.

1 \leq N \leq 100

0 \leq a_i, b_i, c_i, d_i < 2N

a_1, a_2, ..., a_N, c_1, c_2, ..., c_N are all different.

b_1, b_2, ..., b_N, d_1, d_2, ..., d_N are all different.

Input

Input is given from Standard Input in the following format:

N
a_1 b_1
a_2 b_2
:
a_N b_N
c_1 d_1
c_2 d_2
:
c_N d_N

Output

Print the maximum number of friendly pairs.

Sample Input 1

3
2 0
3 1
1 3
4 2
0 4
5 5

Sample Output 1

2

For example, you can pair (2, 0) and (4, 2), then (3, 1) and (5, 5).

Sample Input 2

3
0 0
1 1
5 2
2 3
3 4
4 5

Sample Output 2

2

For example, you can pair (0, 0) and (2, 3), then (1, 1) and (3, 4).

Sample Input 3

2
2 2
3 3
0 0
1 1

Sample Output 3

0

It is possible that no pair can be formed.

Sample Input 4

5
0 0
7 3
2 2
4 8
1 6
8 5
6 9
5 4
9 1
3 7

Sample Output 4

5

Sample Input 5

5
0 0
1 1
5 5
6 6
7 7
2 2
3 3
4 4
8 8
9 9

Sample Output 5

4

Solution in PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
$count = trim(fgets(STDIN));

$getPoints = function($count) {
    $points = [];
    for ($i=0; $i < $count; $i++) {
        list($x, $y) = explode(' ', trim(fgets(STDIN)));
        $points[$x][$y] = true;
    }
    return $points;
};
$redPoints  = $getPoints($count);
$bluePoints = $getPoints($count);
// 赤は降順、青は昇順
krsort($redPoints);
ksort($bluePoints);
foreach ($redPoints as $k => $v) {
    krsort($v);
}
foreach ($bluePoints as $k => $v) {
    ksort($v);
}

$pairCount = 0;
foreach ($bluePoints as $blueX => $blueYArray) {
    foreach ($blueYArray as $blueY => $blueVal) {
        foreach ($redPoints as $redX => $redYArray) {
            if ($redX < $blueX && $blueVal) {
                foreach ($redYArray as $redY => &$redVal) {
                    if ($redY < $blueY && $redVal) {
                        ++$pairCount;
                        $redVal  = false;
                        $blueVal = false;
                    }
                }
            }
        }
    }
}

echo $pairCount;