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 <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <string>
#include <sstream>
#include <complex>
#include <vector>
#include <list>
#include <queue>
#include <deque>
#include <stack>
#include <map>
#include <set>
using namespace std;
typedef long long unsigned int ll;

#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))

int main() {
  int n;
  int a,b;
  scanf("%d\n",&n);

  map<int, int> mapa;
  map<int, int> mapb;
  vector<int> v(2*n+1);
  for (size_t i = 0; i <= 2*n; i++) {
    v[i]=0;
    mapa[i]=-1;
    mapb[i]=-1;
  }
  for (size_t i = 0; i < n; i++) {
    scanf("%d %d\n",&a,&b );
    mapa[a]=b;
  }
  for (size_t i = 0; i < n; i++) {
    scanf("%d %d\n",&a,&b );
    mapb[a]=b;
  }
  int tmp;
  int count=0;
  for (size_t i = 0; i < 2*n; i++) {
    if(mapb[i]!=-1){
      int max=-1;
      int index=-1;
      for (int j = i-1; j >=0; j--) {

        if(mapa[j]!=-1 && mapa[j]<mapb[i] && v[j]!= 1 ){

          if(max<mapa[j]){
            index=j;
            max=mapa[j];
          }
        }

      }
      if(index!=-1){
        v[index]=1;
        count++;
      }
    }
  }
  printf("%d\n",count);
  return 0;
}