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)

// inputに入力データ全体が入る
function Main(input) {
  input = input.split('\n');
  var answer = 0;

  var red = []; 
  var blue = []; 
  var switched = false;

  function Point(x, y) {
    this.x = parseInt(x, 10);
    this.y = parseInt(y, 10);
    this.matches = [];
  }

  for (var i = 1; i < input.length; i++) {
    if (i === parseInt(input[0]) + 1) {
      switched = true;
    }

    if (switched) {
      blue.push(new Point(...input[i].split(' ')));
    } else {
      red.push(new Point(...input[i].split(' ')));
    }
  }

  function isFriendly(red, blue) {
    return red.x < blue.x && red.y < blue.y;
  }


  function findMatches() {
    var matchCount = 0;

    red.forEach(( thisRed, redi ) => {
      if (!thisRed.taken) {
	thisRed.matches = [];
	blue.forEach(( thisBlue, bluei ) => {
	  if (isFriendly(thisRed, thisBlue)) {
	    matchCount++;
	    thisRed.matches.push(thisBlue)
	  }
	})
      }
    });

    return matchCount > 0;
  }

  var hadMatch;

  do {
    hadMatch = findMatches();

    red.forEach((thisRed, redi) => {
      var bestMatch;
      if (!thisRed.taken) {
	thisRed.matches.forEach((thisMatch) => {
	  if (!thisMatch.taken && (!bestMatch || thisMatch.y < bestMatch.y)) {
	    bestMatch = thisMatch;
	  }
	})
	if (bestMatch) {
	  thisRed.taken = true;
	  bestMatch.taken = true;
	  var removeIndex = blue.indexOf(bestMatch);
	  blue.splice(removeIndex, 1);
	  answer++;
	}

      }
    })

  } while (hadMatch);



  // 出力
  console.log(answer);
}
//*この行以降は編集しないでください（標準入出力から一度に読み込み、Mainを呼び出します）
Main(require('fs').readFileSync('/dev/stdin', 'utf8'));