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<iostream>
#include<algorithm>
typedef std::pair<int,int> point;
int main(){
	int n,temp1,temp2;
	int ans1=0,ans2=0;
	point redp1[100],bluep1[100];
	point redp2[100],bluep2[100];
	bool rused1[100],bused1[100];
	bool rused2[100],bused2[100];
	std::cin>>n;
	for(int i=0;i<n;i++){
		std::cin>>temp1>>temp2;//red
		redp1[i].first=temp1,redp1[i].second=temp2;
		redp2[i].second=temp1,redp2[i].first=temp2;
	}
	for(int i=0;i<100;i++){
		rused1[i]=false;
		bused1[i]=false;
		rused2[i]=false;
		bused2[i]=false;
	}
	for(int i=0;i<n;i++){
		std::cin>>temp1>>temp2;//blue
		bluep1[i].first=temp1,bluep1[i].second=temp2;
		bluep2[i].second=temp1,bluep2[i].first=temp2;
	}
	std::sort(redp1,redp1+n);
	std::sort(bluep1,bluep1+n);
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			if(redp1[i].first<bluep1[i+j].first && redp1[i].second<bluep1[i+j].second && !rused1[i] &&!bused1[i+j]){
			ans1++;
			rused1[i]=true,bused1[i+j]=true;
			break;
			}
			else{
			}
		}
	}
	std::sort(redp2,redp2+n);
	std::sort(bluep2,bluep2+n);

	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			if(redp2[i].first<bluep2[i+j].first && redp2[i].second<bluep2[i+j].second && !rused2[i] &&!bused2[i+j]){
			ans2++;
			rused2[i]=true,bused2[i+j]=true;
			break;
			}
			else{
			}
		}
	}
	std::cout<<std::max(ans1,ans2)<<"\n";
}