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>
using namespace std;
using ll = long long;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define pb push_back
const int maxn = 10000;
const int INF32 = 1'050'000'000;
const long long INF64 = 4'000'000'000'000'000'000;
const int MOD7 = 1'000'000'007;
const int MOD9 = 1'000'000'009;

void ERROR(int num) { printf("ERROR%d!\n",num); }
ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
int dx[8]={-1,0,1,0,1,1,-1,-1};
int dy[8]={0,-1,0,1,1,-1,1,-1};

struct P
{
	int x;
	int y;
	bool operator < (const P& A) const{
			return x < A.x;
	}
};
int N;
vector<P> vec1, vec2;
vector<int> check;


int main(){
	cin >> N;
	vec1.resize(N);
	vec2.resize(N);
	rep(i,N) cin >> vec1[i].x >> vec1[i].y;
	rep(i,N) cin >> vec2[i].x >> vec2[i].y;

	sort(vec1.begin(), vec1.end());
	sort(vec2.begin(), vec2.end());

	int k = 0;
	int cnt = 0;
	check.resize(N,0);
	rep(i,N){
		P num = vec2[i];
		int l = lower_bound(vec1.begin(), vec1.end(), num) - vec1.begin();
		int max = -1;
		int index = -1;
		bool ok = 0;
		//cout << "L:" << l << endl;
		rep(j,l){
			if(!check[j]){
				if(vec1[j].y>max && vec1[j].y<num.y){
					max = vec1[j].y;
					index = j;
					ok = 1;
				}
			}
		}
		if(ok){
			//cout << "vec2: " << num.y << " vec1: " << vec1[index].y << endl;
			check[index] = 1;
			cnt++;
		}
	}
	cout << cnt << endl;

}