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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>

void sort(int data[100][3],int n){
  int i,j,temp[2],k;
  for(i = 0; i < n;i++){
    for(j = n-1;j > i;j--){
      if(data[j][0] < data[j-1][0]){
        temp[1] = data[j][1];
        data[j][1] = data[j-1][1];
        data[j-1][1] = temp[1];
        temp[0] = data[j][0];
        data[j][0] = data[j-1][0];
        data[j-1][0] = temp[0];
      }
    }
  }
}



int main()
{
  int ab[100][3],cd[100][3];
  int n;
  int i,j,temp[3];
  int pair = 0;

  scanf("%d",&n);
  for(i = 0;i < n;i++){
    scanf("%d %d",&ab[i][1],&ab[i][0]);
  }
  for(i = 0;i < n;i++){
    scanf("%d %d",&cd[i][1],&cd[i][0]);
    cd[i][2] = 0;
  }

  sort(ab,n);
  sort(cd,n);

  for(i = 0;i < n;i++){
    temp[0] = 0;
    temp[1] = 10001;
    for(j = 0;j < n;j++){
      if(ab[i][0] < cd[j][0]){
        if(ab[i][1] < cd[j][1] && cd[j][2] == 0){
          if(temp[1] > cd[j][1]){
            temp[0] = cd[j][0];
            temp[1] = cd[j][1];
            temp[2] = j;
            if(j == n-1 ){
              cd[j][2] = 1;
              pair++;
              break;
            }
          }
          if(temp[0] < cd[j+1][0]){
            cd[temp[2]][2] = 1;
            pair++;
            break;
          }
        }
      }
    }
  }
  printf("%d\n",pair);

  return(0);
}