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 (Clang 3.8.0) (judge verdict: Wrong Answer)

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

int descending_compare(const void *a, const void *b){
    if (*(int*)a > *(int*)b){
        return -1;
    }else if (*(int*)a == *(int*)b){
        return 0;
    }else{
        return 1;
    }
}

int ascending_compare(const void *a, const void *b){
    if (*(int*)a < *(int*)b){
        return -1;
    }else if (*(int*)a == *(int*)b){
        return 0;
    }else{
        return 1;
    }
}

// array pointer = *a, num of element = n, key key
int lower_bound(int *a, int n, int key){
    int ng, mid, ok;
    ng = -1, ok = n-1;
    while (abs(ok - ng) > 1){
        mid = (ok + ng) / 2;
        if (key <= a[mid]){
            ok = mid;
        }else{
            ng = mid;
        }
    }
    if (a[ok] >= key)return ok;
    return n;
}

//greatest common divisor
unsigned long gcd(unsigned long x, unsigned long y){
    if (y == 0){ 
        return x;
    }else if (x > y){
        return gcd(y, x % y);
    }else{
        return gcd(x, y % x);
    }
}

unsigned long lcm(unsigned long x, unsigned long y){
    unsigned long g = gcd(x, y);
    return x*y/g;

}



long long factorial(int x){
    long long rtn = 1;
    int i;
    for (i = x; i > 1; i--){
        rtn = (rtn*i);
    }
    return rtn;
}




/*unsigned long long pascal[100][100] = {0};
void make_pascal(void){
    for (int i = 0; i < 100; i++){
        pascal[i][0] = 1;
    }
    pascal[1][1] = 1;
    for (int i = 2; i < 100; i++){
        for (int j = 1; j < 100; j++){
           pascal[i][j] = (pascal[i-1][j-1]+pascal[i-1][j]) % mod;
        }
    }
}*/
long long mod = 1000000007;

//x ^ n
long long mod_pow(long long x, long long n){
    long long res = 1;
    for(int i = 0;i < 60; i++){
        if(n >> i & 1) res = res * x % mod;
        x = x * x % mod;
    }
    return res;
}


typedef struct{
    int blue_x;
    int blue_y;
    int used;
}blue;

typedef struct{
    int red_x;
    int red_y;
    int used;
}red;

int blue_ascending_compare(const void *p, const void *q) {
    if ( ((blue*)p)->blue_x == ((blue*)q)->blue_x){
        return ((blue*)p)->blue_y - ((blue*)q)->blue_y;
    }else{
        return ((blue*)p)->blue_x - ((blue*)q)->blue_x;
    }
}

int red_ascending_compare(const void *p, const void *q) {
    if ( ((red*)p)->red_x == ((red*)q)->red_x){
        return ((red*)p)->red_y - ((red*)q)->red_y;
    }else{
        return ((red*)p)->red_x - ((red*)q)->red_x;
    }
}

blue blue_xy[105];
red red_xy[105];

int main(void){
    int n;
    scanf("%d", &n);
    for (int i = 0; i < n; i++){
        scanf("%d %d", &red_xy[i].red_x, &red_xy[i].red_y);
        red_xy[i].used = 0;
    }
    for (int i = 0; i < n; i++){
        scanf("%d %d", &blue_xy[i].blue_x, &blue_xy[i].blue_y);
        blue_xy[i].used = 0;
    }

    qsort(blue_xy, n, sizeof(blue), blue_ascending_compare);
    qsort(red_xy, n, sizeof(red), red_ascending_compare);

    int ans = 0;

/*    for (int i = 0; i < n; i++){
        printf("red %d %d\n", red_xy[i].red_x, red_xy[i].red_y);
    }
    for (int i = 0; i < n; i++){
        printf("blue %d %d\n", blue_xy[i].blue_x, blue_xy[i].blue_y);
    }*/
    for (int i = n-1; i >= 0; i--){
            int max = -1;
            int maxi = -1;
        for (int j = n-1; j >= 0; j--){
            if (red_xy[j].used == 0 && blue_xy[i].blue_x > red_xy[j].red_x && blue_xy[i].blue_y > red_xy[j].red_y){
                if (max < red_xy[j].red_y){
                    max = red_xy[j].red_y;
                    maxi = j;
                }
            }
        }
        if (maxi != -1){
            red_xy[maxi].used = 1;
            ans++;
        }
    }

    printf("%d\n", ans);




    return 0;
}