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>

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

int acsx(const void *p, const void *q){
    return ((point*)p)->x - ((point*)q)->x;
}
int acsy(const void *p, const void *q){
    return ((point*)p)->y - ((point*)q)->y;
}

int main(){
    int i, j, k;
    int N;
    point red[110],blue[110];
    int maxx, maxy, maxpoint;
    int ans=0;

    scanf("%d", &N);
    for(i=0; i<N; i++){
        scanf("%d %d", &red[i].x, &red[i].y);
        red[i].c = 0;
    }
    for(i=0; i<N; i++){
        scanf("%d %d", &blue[i].x, &blue[i].y);
        blue[i].c = 0;
    }

    qsort(red, N, sizeof(point), acsx);
    qsort(blue, N, sizeof(point), acsx);

    for(i=0; i<N; i++){
        maxy=-1;
        maxpoint = -1;
        for(j=0; j<N; j++){
            if(red[j].x < blue[i].x && red[j].c == 0){
                if(red[j].y<blue[i].y && maxy<red[j].y){
                    maxy = red[j].y;
                    maxpoint = j;
                }
            }
        }
        if(maxpoint != -1){
            //printf("%d %d %d %d\n", red[maxpoint].x, red[maxpoint].y, blue[i].x, blue[i].y);
            red[maxpoint].c = 1;
            ans++;
        }
    }

    printf("%d", ans);

    return 0;
}