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)

#include<bits/stdc++.h>
#define mp(a,b) make_pair((a),(b))
#define pii pair<int,int>
#define pdd pair<double,double>
#define pll pair<LL,LL>
#define pb push_back
#define x first
#define y second
#define sqr(x) ((x)*(x))
#define EPS 1e-6
#define mii map<int,int>
#define MEM(x) memset(x,0,sizeof(x))
#define MEMS(x) memset(x,-1,sizeof(x))
#define N 200005
//#define M 1000005
#define pi 3.14159265359
#define cpdd const pdd
#define MAXN 100005
#define INF 0x3f3f3f3f
using namespace std;
typedef long long LL;
vector<int> v[105];
int match[105];
int vis[105];
bool dfs(int a){
	for(auto it:v[a]){
		if(!vis[it]){
			vis[it]=1;
			if(match[it]==-1||dfs(match[it])){
				match[it]=a;
				return true;
			}
		}
	}
	return false;
}
int max_match(int n){
	int cnt=0;
	MEMS(match);
	for(int i=0;i<n;i++){
		MEM(vis);
		if(dfs(i))
			cnt++;
	}
	return cnt;
}
int main(){
	int n;
	scanf("%d",&n);
	pii r[105],b[105];
	for(int i=0;i<n;i++){
		int x,y;
		scanf("%d %d",&x,&y);
		r[i]=mp(x,y);
	}
	for(int i=0;i<n;i++){
		int x,y;
		scanf("%d %d",&x,&y);
		b[i]=mp(x,y);
	}
	for(int i=0;i<n;i++)
		for(int j=0;j<n;j++){
			if(r[i].x<b[j].x&&r[i].y<b[j].y)
				v[i].pb(j);
		}
	printf("%d\n",max_match(n));
}
/*
BC
ACC
AABC
CC
ABC
AACC*/