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: Accepted)

#include<iostream>
#include<vector>
using namespace std;

int main(){
	int n; cin>>n;
	vector<int> a(n),b(n),c(n),d(n);
	for(int i=0;i<n;i++) cin >> a[i] >> b[i];
	for(int i=0;i<n;i++) cin >> c[i] >> d[i];

	int ans=0;
	while(c.size()>0){
		int minxblue=0;
		for(int i=1;i<c.size();i++){
			minxblue=min(c[minxblue],c[i])==c[i]?i:minxblue;
		}
		int maxyred=0;
		bool flag=false;
		for(int i=0;i<a.size();i++){
			if(a[i]<c[minxblue] && b[i]<d[minxblue]){
				if(!flag) maxyred=i;
				maxyred=max(b[i],b[maxyred])==b[i]?i:maxyred;
				flag=true;
			}
		}
		if(flag){
			ans++;
			a.erase(a.begin()+maxyred);
			b.erase(b.begin()+maxyred);
		}
		c.erase(c.begin()+minxblue);
		d.erase(d.begin()+minxblue);
	}
	cout << ans << endl;
}