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;

#define int long long
#define MAX 110

int N;
vector<pair<int,int> > red, blue, fuga;
int used[MAX], hoge[MAX][MAX];

signed main(){

  int a, b, ans = 0;

  cin>>N;

  for(int i = 0; i < N; i++){
    cin>>a>>b;
    red.push_back(make_pair(a,b));
  }

  for(int i = 0; i < N; i++){
    cin>>a>>b;
    blue.push_back(make_pair(a,b));
    fuga.push_back(make_pair(0,i));
  }

  sort(red.begin(), red.end());
  sort(blue.begin(), blue.end());

  for(int i = 0; i < N; i++){
    fuga[i].second = i;
    for(int j = 0; j < N; j++){
      if(red[i].first < blue[j].first && red[i].second < blue[j].second){
	hoge[i][j] = true;
	fuga[i].first++;
      }
    }
  }
  sort(fuga.begin(),fuga.end());

  for(int k = 0; k < N; k++){

    if(fuga[0].first){
      
      int temp = 0;
      
      for(int i = 0; i < N; i++){
	if(hoge[fuga[0].second][i] == 1){
	  temp = i;
	  break;
	}
      }
      for(int i = 0; i < N; i++){
	if(hoge[fuga[i].second][temp] == 1){
	fuga[i].first--;
	}
      }
     ans++;
    }
    
    fuga.erase(fuga.begin());
    
    sort(fuga.begin(),fuga.end());
  }
  
 
  cout<<ans<<endl;
  
  return 0;
}