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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>

typedef struct
{
	int x;
	int y;
} plot;


int distance_point(plot a, plot b)
{
	return (a.x - b.x)*(a.x - b.x) + (a.y - b.y)*(a.y - b.y);
}

int fcmp(const void *a, const void *b)
{
		return (((plot *)a)->x + ((plot *)a)->y) - (((plot *)b)->x + ((plot *)b)->y);
}

int main(void)
{
	int num_point;
	plot *red, *blue;
	int i, j;
	int distance, distance_id;
	int ans = 0;

	scanf("%d", &num_point);

	red = (plot *)malloc(sizeof(plot) * num_point);
	blue = (plot *)malloc(sizeof(plot) * num_point);
	for(i = 0; i < num_point; i++)
		scanf("%d %d", &red[i].x, &red[i].y);
	for(i = 0; i < num_point; i++)
		scanf("%d %d", &blue[i].x, &blue[i].y);

	qsort(red, num_point, sizeof(plot), fcmp);

	for(i = 0; i < num_point; i++)
	{
		for(j = 0; j < num_point; j++)
		{
			if(blue[j].x-red[i].x>0 && blue[j].y-red[i].y>0)
			{
				distance = distance_point(blue[j], red[i]);
				distance_id = j;
				ans++;
				break;
			}
		}

		if(j == num_point)
			continue;

		for(j = 0; j < num_point; j++)
		{
			if(blue[j].x-red[i].x>0 && blue[j].y-red[i].y>0 && distance_point(blue[j], red[i]) < distance)
			{
				distance = distance_point(blue[j], red[i]);
				distance_id = j;
			}
		}
		if(j == num_point-1)
			num_point--;
		else
		{
			blue[distance_id].x = blue[num_point-1].x;
			blue[distance_id].y = blue[num_point-1].y;
		}
	}

	printf("%d", ans);

	free(red);
	free(blue);

	return 0;
}