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>

struct red{
    int x;  
    int y;
    int flag;
};

struct blue{
    int x;  
    int y;
};

void quicksortr(struct red data[],int left,int right);
void quicksortb(struct blue data[],int left,int right);

int main()
{
	int n,i,j,k,ans=0;
	struct red rp[100]={0,0,0};
	struct blue bp[100]={0,0};
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d %d",&(rp[i].x),&(rp[i].y));
	}
	for(i=0;i<n;i++)
	{
		scanf("%d %d",&(bp[i].x),&(bp[i].y));
	}
	quicksortr(rp,0,n-1);
	quicksortb(bp,0,n-1);
	for(i=0;i<n;i++)//blue
	{
		for(j=0;j<n;j++)//red
		{
			if(((bp[i].x>rp[j].x)&&(bp[i].y>rp[j].y))&&(rp[j].flag==0))
			{
				rp[j].flag=1;
				ans++;
				break;
			}
		}
	}
	printf("%d",ans);
}

void quicksortr(struct red data[],int left,int right)
{
	int i,j;
	struct red std,work;
	if(left<right)
	{
		i=left,j=right;
		std=data[(i+j)/2];//基準
		do
		{
			while(data[i].y > std.y)i++;
			while(data[j].y < std.y)j--;
			if(i<=j)
			{
				if(i<j)
				{
					work=data[i];
					data[i]=data[j];
					data[j]=work;
				}
				i++; j--;
			}
		}while(i<=j);
		if(left<j)quicksortr(data,left,j);
		if(i<right)quicksortr(data,i,right);
	}
}
void quicksortb(struct blue data[],int left,int right)
{
	int i,j;
	struct blue std,work;
	if(left<right)
	{
		i=left,j=right;
		std=data[(i+j)/2];//基準
		do
		{
			while(data[i].x < std.x)i++;
			while(data[j].x > std.x)j--;
			if(i<=j)
			{
				if(i<j)
				{
					work=data[i];
					data[i]=data[j];
					data[j]=work;
				}
				i++; j--;
			}
		}while(i<=j);
		if(left<j)quicksortb(data,left,j);
		if(i<right)quicksortb(data,i,right);
	}
}