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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		FastScanner in = new FastScanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}

	static class TaskC {
		public void solve(int testNumber, FastScanner in, PrintWriter out) {
			int n = in.nextInt();
			int[] a = new int[n];
			int[] b = new int[n];
			int[] c = new int[n];
			int[] d = new int[n];
			for (int i = 0; i < n; i++) {
				a[i] = in.nextInt();
				b[i] = in.nextInt();
			}
			for (int i = 0; i < n; i++) {
				c[i] = in.nextInt();
				d[i] = in.nextInt();
			}
			boolean[][] g = new boolean[n][n];
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < n; j++) {
					if (a[i] < c[j] && b[i] < d[j]) {
						g[i][j] = true;
					}
				}
			}
			out.println(bipartiteMatching(g));
		}

		private int bipartiteMatching(boolean[][] g) {
			int n = g.length;
			if (n == 0) {
				return 0;
			}
			int m = g[0].length;
			boolean[] was = new boolean[n];
			int[] pair = new int[m];
			Arrays.fill(pair, -1);
			int res = 0;
			for (int i = 0; i < n; i++) {
				Arrays.fill(was, false);
				if (dfs(i, g, was, pair)) {
					++res;
				}
			}
			return res;
		}

		private boolean dfs(int i, boolean[][] g, boolean[] was, int[] pair) {
			if (was[i]) {
				return false;
			}
			was[i] = true;
			for (int j = 0; j < g[i].length; j++) {
				if (!g[i][j]) {
					continue;
				}
				if (pair[j] < 0 || dfs(pair[j], g, was, pair)) {
					pair[j] = i;
					return true;
				}
			}
			return false;
		}

	}

	static class FastScanner {
		private BufferedReader in;
		private StringTokenizer st;

		public FastScanner(InputStream stream) {
			in = new BufferedReader(new InputStreamReader(stream));
		}

		public String next() {
			while (st == null || !st.hasMoreTokens()) {
				try {
					String rl = in.readLine();
					if (rl == null) {
						return null;
					}
					st = new StringTokenizer(rl);
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

	}
}