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: Accepted)

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

typedef struct {
	int x;
	int y;
  int check;
} S_POINT;

int cmpR(const void * n1, const void * n2)
{
	if (((S_POINT *)n1)->y > ((S_POINT *)n2)->y)
	{
		return -1;
	}
	else if (((S_POINT *)n1)->y < ((S_POINT *)n2)->y)
	{
		return 1;
	}
	else
	{
		return 0;
	}
}

int cmpB(const void * n1, const void * n2)
{
	if (((S_POINT *)n1)->x > ((S_POINT *)n2)->x)
	{
		return 1;
	}
	else if (((S_POINT *)n1)->x < ((S_POINT *)n2)->x)
	{
		return -1;
	}
	else
	{
		return 0;
	}
}

int main(void) {

  int n;
  scanf("%d", &n);
  S_POINT red[n],blue[n];
  for (int i = 0; i < n; i++) {
    scanf("%d %d", &red[i].x, &red[i].y);
    red[i].check = 0;
  }
  for (int i = 0; i < n; i++) {
    scanf("%d %d", &blue[i].x, &blue[i].y);
    blue[i].check = 0;
  }
  qsort(red, n, sizeof(S_POINT), cmpR);
  qsort(blue, n, sizeof(S_POINT), cmpB);
  int pairs = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (red[j].check == 0 && red[j].x < blue[i].x && red[j].y < blue[i].y) {
        red[j].check = 1;
        pairs++;
        break;
      }
    }
  }
  printf("%d\n", pairs);

  return 0;
}