output_description: Print the maximum number of friendly pairs.
  
  * * *
input_description: 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
attempt: #include<stdio.h>
  #include<stdlib.h>
  #include<string.h>
  
  #define NEW(p,n){p=malloc((n)*sizeof(p[0]));if(p==NULL){printf("not enough memory\n");exit(1);};}
  //pの型の変数n個の要素分のメモリを確保し、そのアドレスをpに代入するマクロ
  
  #define MAX(a, b) ((a) > (b) ? (a) : (b))
  #define MIN(a, b) ((a) < (b) ? (a) : (b))
  #define SWAP(type, x, y) do { type tmp = x; x = y; y = tmp; } while (0)
  
  #define MOD 1000000007 
  
  typedef struct{
      int x;
      int y;
      int flg;
  }data;
  
  //x軸の昇順
  int xasc(const void* a, const void* b){
      data p = *(data*)a;
      data q = *(data*)b;
      if(p.x!=q.x) return p.x-q.x;
      else return p.y-q.y;
  }
  
  //y軸の降順
  int ydesc(const void* a, const void* b){
      data p = *(data*)a;
      data q = *(data*)b;
      if(p.y!=q.y) return q.y-p.y;
      else return q.x-p.x;
  }
  
  int main(void){
      int N;
      scanf("%d",&N);
  
      //A[0]~A[N-1]に格納する
      data* red;
      NEW(red,N);
      for(int i=0;i<N;i++){
          scanf("%d%d",&red[i].x,&red[i].y);
          red[i].flg=0;
      }
      qsort(red,N,sizeof(data),ydesc);
  
      data* blue;
      NEW(blue,N);
      for(int i=0;i<N;i++){
          scanf("%d%d",&blue[i].x,&blue[i].y);
          blue[i].flg=0;
      }
      qsort(blue,N,sizeof(data),xasc);
  
      int ans=0;
      for(int i=0;i<N;i++){
          for(int j=0;j<N;j++){
              if(red[j].flg) continue;
              if(red[j].x<blue[i].x && red[j].y<blue[i].y){
                  ans++;
                  red[j].flg=1;
                  break;
              }
          }
      }
      printf("%d\n",ans);
  
      return 0;
  }
problem_description: 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.
samples: [{"input": "3\n    2 0\n    3 1\n    1 3\n    4 2\n    0 4\n    5 5", "output": "2\n    \n\nFor example, you can pair (2, 0) and (4, 2), then (3, 1) and (5, 5).\n\n* * *"}, {"input": "3\n    0 0\n    1 1\n    5 2\n    2 3\n    3 4\n    4 5", "output": "2\n    \n\nFor example, you can pair (0, 0) and (2, 3), then (1, 1) and (3, 4).\n\n* * *"}, {"input": "2\n    2 2\n    3 3\n    0 0\n    1 1", "output": "0\n    \n\nIt is possible that no pair can be formed.\n\n* * *"}, {"input": "5\n    0 0\n    7 3\n    2 2\n    4 8\n    1 6\n    8 5\n    6 9\n    5 4\n    9 1\n    3 7", "output": "5\n    \n\n* * *"}, {"input": "5\n    0 0\n    1 1\n    5 5\n    6 6\n    7 7\n    2 2\n    3 3\n    4 4\n    8 8\n    9 9", "output": "4"}]