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>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define PI 				acos(-1)
#define mp				make_pair
#define pb				push_back
#define all(a)			(a).begin(), (a).end()
#define sz(a)			a.size()
#define srt(a)			sort(all(a))
#define mem(a, h)		memset(a, (h), sizeof(a))
#define f 				first
#define s 				second
#define MOD1			998244353
#define fore(i, b, e)	for(int i = b; i < e; i++)
#define forg(i, b, e, m)	for(int i = b; i < e; i+=m)
int in(){int r=0,c;for(c=getchar();c<=32;c=getchar());if(c=='-') return -in();for(;c>32;r=(r<<1)+(r<<3)+c-'0',c=getchar());return r;}

using namespace std;
using namespace __gnu_pbds;

typedef long long 		ll;
typedef unsigned long long 		ull;
typedef pair<int, int>  ii;
typedef vector<int>     vi;
typedef vector<ii>      vii;
typedef vector<ll>      vll;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//find_by_order kth largest  order_of_key <
const int tam = 100010;
const int MOD = 1e9+7;
const double EPS = 1e-9;

int main()
{
	ios::sync_with_stdio(0); cin.tie(0);
	//freopen("qwe.txt", "r", stdin);
	int n;
	cin>>n;
	pair<int, int> ar1[n], ar2[n];
	bool mar[n];
	mem(mar, 0);
	fore(i, 0, n) cin>>ar1[i].f>>ar1[i].s;
	fore(i, 0, n) cin>>ar2[i].f>>ar2[i].s;
	sort(ar2, ar2 + n);
	int may, mayo;
	int res = 0;
	fore(i, 0, n)
	{
		may = -1;
		mayo = -MOD;
		fore(j, 0, n)
		{
			if(!mar[j] && ar1[j].f < ar2[i].f && ar1[j].s < ar2[i].s)
			{
				if(ar1[j].s > mayo)
				{
					mayo = ar1[j].s;
					may = j;
				}
			}
		}
		if(may > -1)
		{
			mar[may] = 1;
			res++;
		}
	}
	cout<<res<<'\n';
	return 0;
}

// read the question correctly (is y a vowel? what are the exact constraints?)
// look out for SPECIAL CASES (n=1?) and overflow (ll vs int?) ARRAY OUT OF BOUNDSS2