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 JavaScript (node.js v5.12) (judge verdict: Wrong Answer)

var lines = [];
var readline = require('readline');

var rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
});

rl.on('line', function (x) {
    lines.push(x);
});

rl.on('close', function () {
    var N = Number(lines[0]);

    var ab = [];
    for (var i = 1; i - 1 < N; i++) {
        var t = lines[i].split(" ");
        ab.push([t[0], t[1]])
    }

    var cd = [];
    for (var i = N + 1; i - (N + 1) < N; i++) {
        cd.push(lines[i].split(" "));
    }

    ab.sort((a, b) => a[1] - b[1] || a[0] - b[0]);
    cd.sort((a, b) => a[1] - b[1] || a[0] - b[0]);
    
    console.log(cd)
    console.log(ab)

    var used = Array(N).fill(false);
    var ans = 0;

    for (var i = 0; i < N; i++) {
        var x1 = Number(cd[i][0]); var y1 = Number(cd[i][1]);
        var d_min = Infinity

        for (var j = 0; j < N; j++) {
            var x2 = Number(ab[j][0]); var y2 = Number(ab[j][1]);
            if (x2 < x1 && y2 < y1 && used[j] === false) {
                var d = y1 - y2;
                if (d < d_min) { d_min = d; var k = j; }
            }
        }
        if (d_min !== Infinity) { used[k] = true; ans++; }
    }
    console.log(ans);
});