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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
const int maxn = 107;
struct node{
	int x,y;
}red[maxn],blu[maxn];
bool cmp(node a,node b){
	if(a.x == b.x) return a.y < b.y;
	return a.x < b.x;
}
bool bmp(node a,node b){
	if(a.y == b.y) return a.x < b.x;
	return a.y > b.y;
}
int vis[maxn] = {0};
int main(){
	int n;
	scanf("%d",&n);
	for(int i = 1;i <= n;i++){
		int x,y;
		scanf("%d %d",&x,&y);
		red[i].x = x;
		red[i].y = y;
	}
	for(int i = 1;i <= n;i++){
		int x,y;
		scanf("%d %d",&x,&y);
		blu[i].x = x;
		blu[i].y = y;
	}
	sort(red+1,red+1+n,bmp);
	sort(blu+1,blu+1+n,cmp);
	int cnt = 0;
	for(int i = n;i >= 1;i--){
		for(int j = 1;j <= n;j++){
			if(blu[i].x >= red[j].x && blu[i].y >= red[j].y && !vis[j]){
				cnt++;
				vis[j] = 1;
				break;
			}
		}
	}
	printf("%d\n",cnt);
	return 0;
}