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>

void SWAP(int *x, int *y){
	int temp = *x;
	*x = *y;
	*y = temp;
}

int main(void){
	int num, i, j, Ans = 0;
	int ***MainArray;
	scanf("%d",&num);
	MainArray = (int***)malloc(sizeof(int**)*2);
	for(i=0;i<2;i++){
		MainArray[i] = (int**)malloc(sizeof(int*)*num);
		for(j=0;j<num;j++){
			MainArray[i][j] = (int*)malloc(sizeof(int)*2);
			scanf("%d %d", &MainArray[i][j][0], &MainArray[i][j][1]);
		}
	}
	for(j=0;j<num-1;j++){
		for(i=0;i<num-1;i++){
			if(abs(MainArray[1][i][0] - MainArray[1][i][1]) < abs(MainArray[1][i+1][0] - MainArray[1][i+1][1])){
				SWAP(&MainArray[1][i][0], &MainArray[1][i+1][0]);
				SWAP(&MainArray[1][i][1], &MainArray[1][i+1][1]);
			}else if(abs(MainArray[1][i][0] - MainArray[1][i][1]) == abs(MainArray[1][i+1][0] - MainArray[1][i+1][1])){
				if((MainArray[1][i][0] + MainArray[1][i][1]) > (MainArray[1][i+1][0] + MainArray[1][i+1][1])){
					SWAP(&MainArray[1][i][0], &MainArray[1][i+1][0]);
					SWAP(&MainArray[1][i][1], &MainArray[1][i+1][1]);
				}
			}
		}
	}
	for(i=0;i<num;i++){
		int memory[2] = {100, -1};
		for(j=0;j<num;j++){
			if(MainArray[1][i][0] != -1 && MainArray[0][j][0] != -1){
				if(MainArray[1][i][0] > MainArray[0][j][0] && MainArray[1][i][1] > MainArray[0][j][1]){
					if ((MainArray[1][i][0] - MainArray[0][j][0] + MainArray[1][i][1] - MainArray[0][j][1]) < memory[0]){
						memory[0] = MainArray[1][i][0] - MainArray[0][j][0] + MainArray[1][i][1] - MainArray[0][j][1];
						memory[1] = j;
					}
				}
			}
		}
		if(memory[1] != -1){
			MainArray[1][i][0] = -1;
			MainArray[0][memory[1]][0] = -1;
			MainArray[1][i][1] = -1;
			MainArray[0][memory[1]][1] = -1;
			Ans++;
		}
	}
	printf("%d",Ans);
}