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)

//
//  main.cpp
//  C - 2D Plane 2N Points
//
//  Created by 谢威宇 on 2018/3/17.
//  Copyright © 2018年 Ervin's Studio. All rights reserved.
//

#include <iostream>
#include <cstring>
using namespace std;
struct _p{
    int x,y;
}red[200],blue[200];
int line[102][102]={0};
int girl[102]={0};
int used[102]={0};

bool found(int x,int n)
{
    for(int i=1; i<=n; i++)
    {
        if(line[x][i]&&!used[i])
        {
            used[i]=1;
            if(girl[i]==0||found(girl[i],n))
            {
                girl[i]=x;
                return 1;
            }
        }
    }
    return 0;
}

int main(int argc, const char * argv[]) {
    int n;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        int x,y;
        cin>>x>>y;
        red[i].x=x;
        red[i].y=y;
    }
    for(int i=1;i<=n;i++)
    {
        int x,y;
        cin>>x>>y;
        blue[i].x=x;
        blue[i].y=y;
        for(int j=1;j<=n;j++)
        {
            if(red[j].x<x&&red[j].y<y)
            {line[j][i]=1;}
        }
    }
    
//    for(int i=1;i<=n;i++)
//    {
//        for(int j=1;j<=n;j++)
//            cout<<line[i][j]<<" ";
//        cout<<endl;
//    }
    int ans=0;
    for(int i=1;i<=n;i++)
    {
        memset(used,0,sizeof(used));
        if(found(i,n))
            ans++;
    }
    cout<<ans<<endl;
    
    return 0;
}