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<cmath>
#include<algorithm>
#include<ctime>
#include<cstring>
#define ll long long
#define ld long double
using namespace std;

struct Node{
	int x;
	int y;
}a[1000],b[1000];

int cmp(Node u,Node v){
	if (u.x==v.x) return u.y<v.y;
	return u.x<v.x;
}
int done[1000];

int main(){
	srand((unsigned int)time(NULL));
	int n;
	cin>>n;
	for (int i=1;i<=n;i++){
		cin>>a[i].x>>a[i].y;
	}
	for (int i=1;i<=n;i++){
		cin>>b[i].x>>b[i].y;
	}
	
	sort(a+1,a+n+1,cmp);
	sort(b+1,b+n+1,cmp);
	
	int ans=0;
	
	for (int i=1;i<=n;i++){
		for (int j=1;j<=n;j++){
			if (!done[j]&&cmp(a[i],b[j])){
				done[j]=1;
				ans++;
				break;
			}
		}
	}
	
	for (int loop=1;loop<=3000;loop++){
		random_shuffle(a+1,a+n+1);
		random_shuffle(b+1,b+n+1);
		int cnt=0;
		for (int i=1;i<=n;i++){
			if(cmp(a[i],b[i])){
				cnt++;
			}
		}
		ans=max(ans,cnt);
	}
	
	cout<<ans<<endl;	
}