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: Wrong Answer)

#include <bits/stdc++.h>

using namespace std;

void debug(vector<vector<int> > &a, int n) {
  printf("Debug start\n");
  for (int i=0; i<n; i++) {
    for (int j=0; j<2; j++) {
      printf("%d ", a[i][j]);  
    }
    printf("\n");
  }
  printf("Debug end\n");
}

int main() {
  int n;
  scanf("%d", &n);
  vector<vector<int> > ab(n);
  vector<vector<int> > cd(n);
  for (int i=0; i<n; i++) {
    for (int j=0; j<2; j++) {
      int x;
      scanf("%d", &x);
      ab[i].push_back(x);
    }
  }

  for (int i=0; i<n; i++) {
    for (int j=0; j<2; j++) {
      int x;
      scanf("%d", &x);
      cd[i].push_back(x);
    }
  }

  sort(ab.begin(), ab.end(), [](const std::vector< int >& a, const std::vector< int >& b){ return a[0] > b[0]; } );
  sort(cd.begin(), cd.end(), [](const std::vector< int >& a, const std::vector< int >& b){ return a[0] < b[0]; } );

  int ans = 0;
  vector<bool> ab_check(n);
  vector<bool> cd_check(n);
  for (int i=0; i<n; i++) {
    ab_check[i] = true;
    cd_check[i] = true;
  }

  for (int i=0; i<n; i++) {
    for (int j=0; j<n; j++) {
      // printf("ab: (%d, %d), cd: (%d, %d)\n", ab[i][0], ab[i][1], cd[j][0], cd[j][1]);
      if ((ab[i][0] < cd[j][0]) && ab[i][1] < cd[j][1] && ab_check[i] && cd_check[j]) {
        ans++;
        ab_check[i] = false;
        cd_check[j] = false;
        // printf("ANS+1 %d \n", ans);
      }
    }
  }

  // debug(ab, n);

  printf("%d\n", ans);
  return 0;
}