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: Accepted)

#include<stdio.h>
#include<stdlib.h>
#include<math.h>

typedef long long int int64;

#define MAX(a,b) ((a)>(b)?(a):(b))
#define MIN(a,b) ((a)<(b)?(a):(b))
#define ABS(a) ((a)>(0)?(a):-(a))

typedef struct dpoint{
  int x,y;
} point;

void isort(point *a,int n){
  int i,j;
  for(i=1;i<n;i++){
    point t=a[i];
    j=i-1;
    while(j>=0 && t.x<a[j].x){
      a[j+1]=a[j];
      j--;
    }
    a[j+1]=t;
  }
  return;
}

void run(void){
  int n;
  scanf("%d",&n);
  point *a=(point *)malloc(sizeof(point)*n);
  point *b=(point *)malloc(sizeof(point)*n);
  int i;
  for(i=0;i<n;i++){
    int x,y;
    scanf("%d%d",&x,&y);
    a[i].x=x;
    a[i].y=y;
  }
  for(i=0;i<n;i++){
    int x,y;
    scanf("%d%d",&x,&y);
    b[i].x=x;
    b[i].y=y;
  }
  isort(a,n);
  isort(b,n);
  int cnt=0;
  for(i=n-1;i>=0;i--){
    int j;
    for(j=0;j<n;j++){
      if(a[i].x<b[j].x && a[i].y<b[j].y) break;
    }
    if(j==n) continue;
    int min=j;
    for(j=min+1;j<n;j++){
      if(a[i].y<b[j].y && b[min].y>b[j].y) min=j;
    }
    cnt++;
    b[min].y=-1;
  }
  printf("%d\n",cnt);
  return;
}

int main(void){
  run();
  return 0;
}