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: Time Limit Exceeded)

function main(input) {
    var n = input[0]-0;
    var alist = [];
    var blist = [];
    for(var i=1;i<=n;i++){
        alist.push(input[i].split(" ").map(v=>v-0));
        blist.push(input[i+n].split(" ").map(v=>v-0));
    }
    var nodes = [];
    for(var i=0;i<n;i++){
        nodes[i] = [];
        for(var j=0;j<n;j++){
            if(alist[i][0] < blist[j][0] && alist[i][1] < blist[j][1])
                nodes[i].push(j);
        }
    }
    console.log(calc(nodes, {}, 0,0));
    

}

function calc(nodes, usedmap, cnt, now){
    if(nodes.length == now ) return cnt;
    var ans = 0;
    for(var i=0;i<nodes[now].length;i++){
        if(!usedmap[nodes[now][i]]){
            var nextusedmap = JSON.parse(JSON.stringify(usedmap));
            nextusedmap[nodes[now][i]] = true;
            ans = Math.max(ans, calc(nodes, nextusedmap, cnt+1, now+1));
        }
    }
    ans = Math.max(ans, calc(nodes, JSON.parse(JSON.stringify(usedmap)), cnt, now+1));
    return ans;    
}
main(require('fs').readFileSync('/dev/stdin', 'utf8').trim().split("\n"));