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 <iostream>
# include <algorithm>
# include <vector>
# include <string>
# include <set>
# include <map>
# include <cmath>
# include <iomanip>
# include <functional>
# include <utility>
# include <stack>
# include <queue>
# include <list>
# include <tuple>
# include <unordered_map>
# include <numeric>
# include <complex>
# include <bitset>
# include <random>
# include <chrono>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
typedef pair<LL, LL> P;
constexpr int INF = 2000000000;
constexpr int HINF = INF / 2;
constexpr double DINF = 100000000000000000.0;
constexpr long long LINF = 9223372036854775807;
constexpr long long HLINF = 4500000000000000000;
const double PI = acos(-1);
int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
# define ALL(x)      (x).begin(),(x).end()
# define UNIQ(c)     (c).erase(unique(ALL((c))),(c).end())
# define mp          make_pair
# define eb          emplace_back
# define FOR(i,a,b)  for(int i=(a);i<(b);i++)
# define RFOR(i,a,b) for(int i=(a);i>=(b);i--)
# define REP(i,n)    FOR(i,0,n)
# define INIT        std::ios::sync_with_stdio(false);std::cin.tie(0)

struct edge { int to, cap, rev; };

const int MAX_SIZE = 202;

vector<edge>G[MAX_SIZE];

void add_edge(int from, int to, int cap) {
	G[from].push_back(edge { to, cap, (int)G[to].size() });
	G[to].push_back(edge { from, 0, (int)G[from].size() - 1 });
}

bool used[MAX_SIZE];
int dfs(int p, int t, int f) {
	if (p == t)return f;
	used[p] = true;

	for (int i = 0; i<G[p].size(); i++) {
		edge &e = G[p][i];
		if (used[e.to] || e.cap == 0)continue;
		int _f = dfs(e.to, t, min(f, e.cap));
		if (_f) {
			e.cap -= _f;
			G[e.to][e.rev].cap += _f;
			return _f;
		}
	}

	return 0;
}

int max_flow(int s, int t) {
	int flow = 0;
	while (true) {
		fill_n(used, MAX_SIZE, false);
		int f = dfs(s, t, INF);
		if (f)flow += f;
		else return flow;
	}
}

vector<pair<int, int>>r, b;
int n;
int main() {
	cin >> n;
	int s = 2 * n, t = s + 1;
	REP(i, n) {
		int c, d;
		cin >> c >> d;
		r.emplace_back(mp(c, d));
		add_edge(s, i, 1);
	}
	REP(i, n) {
		int c, d;
		cin >> c >> d;
		b.emplace_back(mp(c, d));
		add_edge(n + i, t, 1);
	}
	REP(i, n)REP(j, n) {
		if (r[i].first < b[j].first&&r[i].second < b[j].second)add_edge(i,j+n,1);
	}
	cout << max_flow(s,t) << endl;
}