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 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <fstream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <cstdlib>
#include <cstdio>
#include <string>
#include <cstring>
#include <cassert>
#include <utility>
#include <iomanip>
#include <chrono>
#include <random>
#include <bitset>

using namespace std;

#define sz(x) (int) x.size()
#define unique(x) x.erase(unique(x.begin(), x.end()), x.end())
#define all(a) a.begin(), a.end()
#define sqr(x) ((x) * (x)) 
#define y1 aksjdaskdjksjfksdjf
#define left kdnvldvoiwejifejg
#define right lkdsjflksdjfdjfk
#define prev asdasfsadjkjsdfjs
#define tm aklsjdasjdasjdkdjjf
#define lcm hddalkwjeidjjhasda
#define random_shuffle asdasdd

const int MAXN = 305;

int n;
vector <int> red[MAXN], blue[MAXN];

int main() { 

  cin >> n;
  for (int i = 0; i < n; i++) {
    int a, b;
    scanf("%d %d", &a, &b);
    red[a].push_back(b);
  }
  for (int i = 0; i < n; i++) {
    int c, d;
    scanf("%d %d", &c, &d);
    blue[c].push_back(d);
  }

  int ans = 0;
  multiset<int> st;
  for (int i = 0; i < 2 * n; i++) {
    sort(all(blue[i]));
    for (int y : blue[i]) {
      auto it = st.upper_bound(y);
      if (it != st.begin()) {
        it--;
        ans++;
        st.erase(it);
      }
    }
    for (int y : red[i]) {
      st.insert(y);
    }
  }

  cout << ans << endl;

  return 0;
}