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: Runtime Error)

#include<bits/stdc++.h>
using namespace std;

vector<pair<int,int> > v[2];
vector<pair<int,int> > sel;
vector<int> whatsel[210];
map<int,bool> mp;

main()
{
	int n;
	scanf("%d",&n);
	for(int i=0;i<n;i++)
	{
		int a,b;
		scanf("%d %d",&a,&b);
		v[0].push_back(make_pair(a,b));
	}
	for(int i=0;i<n;i++)
	{
		int a,b;
		scanf("%d %d",&a,&b);
		v[1].push_back(make_pair(a,b));
	}
	sort(v[0].begin(),v[0].end());
	sort(v[1].begin(),v[1].end());
	for(int i=0;i<n;i++)
	{
		int ti=0;
		for(int j=0;j<n;j++)
		{
			if(v[0][i].first<v[1][j].first&&v[0][i].second<v[1][j].second)
			{	
				if(ti==0)
				{
					sel.push_back(make_pair(0,i));
					ti=1;
				}
				sel[i].first++;
				whatsel[i].push_back(j);
			}
		}
	}
	int ans=0;
	sort(sel.begin(),sel.end());
	for(int i=0;i<sel.size();i++)
	{
		//printf("%d,se:%d\n",i,sel[i].second);
		for(int j=0;j<whatsel[sel[i].second].size();j++)
		{
			if(mp[whatsel[sel[i].second][j]]==0)
			{
				mp[whatsel[sel[i].second][j]]=1;
				ans++;
				break;
			}
		}
	}
	printf("%d\n",ans);
}