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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>

#define x first
#define y second

using namespace std;

const int N = 1e3 + 7;

struct node
{
    int x, y;
};

pair<int, int> a[N], b[N];
map<pair<int, int>, bool> u;

int ans;

bool cmp(pair<int, int>a, pair<int, int>b)
{
    if (a.y > b.y)return 1;
    else if (a.y == b.y)
        return (a.x > b.x);

    return 0;
}

main()
{
    int n;

    cin >> n;

    for (int i = 0; i < n; i++)
    {
        cin >> a[i].x >> a[i].y;
    }
    for (int i = 0; i < n; i++)
    {
        cin >> b[i].x >> b[i].y;
    }

    sort(b, b + n);
    sort(a, a + n, cmp);

    for (int i = 0; i < n; i++)
    {
        int mx = 0, my = 0;
        for (int j = 0; j < n; j++)
        {
            if (b[i].x > a[j].x && b[i].y > a[j].y && !u[a[j]])
            {
                ans++;
                u[a[j]] = 1;
                break;
            }
        }
    }

    cout << ans;
}