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 PyPy3 (2.4.0) (judge verdict: Wrong Answer)

import sys
from io import StringIO
import unittest

def resolve():
    # ★get input
    n = int(input())
    red = [[int(i) for i in input().split()] for j in range(n)]
    blue = [[int(i) for i in input().split()] for j in range(n)]

    # # redに次元を追加。(以下の処理で、redの内容が更新される。
    # for i in red:
    #     i.append(0)

    for i in red:

        matching_count = 0

        for j in blue:
            if i[0] < j[0] and i[1] < j[1]:
                matching_count += 1

        i.append(matching_count)

    # redをマッチング数の昇順でソートする
    red.sort(key=lambda xx: xx[2])

    ans = 0
    for i in red:
        for j in blue:
            if i[0] < j[0] and i[1] < j[1]:
                blue.remove(j)
                ans += 1
                break

    print(ans)
    # ★exec
    # 各点が作れるペア数を確認。



class TestClass(unittest.TestCase):
    def assertIO(self, input, output):
        stdout, stdin = sys.stdout, sys.stdin
        sys.stdout, sys.stdin = StringIO(), StringIO(input)
        resolve()
        sys.stdout.seek(0)
        out = sys.stdout.read()[:-1]
        sys.stdout, sys.stdin = stdout, stdin
        self.assertEqual(out, output)
    def test_入力例_1(self):
        input = """3
2 0
3 1
1 3
4 2
0 4
5 5"""
        output = """2"""
        self.assertIO(input, output)
    def test_入力例_2(self):
        input = """3
0 0
1 1
5 2
2 3
3 4
4 5"""
        output = """2"""
        self.assertIO(input, output)
    def test_入力例_3(self):
        input = """2
2 2
3 3
0 0
1 1"""
        output = """0"""
        self.assertIO(input, output)
    def test_入力例_4(self):
        input = """5
0 0
7 3
2 2
4 8
1 6
8 5
6 9
5 4
9 1
3 7"""
        output = """5"""
        self.assertIO(input, output)
    def test_入力例_5(self):
        input = """5
0 0
1 1
5 5
6 6
7 7
2 2
3 3
4 4
8 8
9 9"""
        output = """4"""
        self.assertIO(input, output)

if __name__ == "__main__":
    # unittest.main()
    resolve()