10
-2 1
2 -2
-1 -2
0 0
2 -1
0 -2
2 2
0 2
-1 -1
1 -2
 40
-8 24
2 -1
1 -18
72 -70
5 -4
-308 436
-19 40
36 -35
-178 265
-1 2
-7 30
-1 0
3 -2
200 -285
17 -16
-35 74
0 -4
-86 106
-1 4
-7 6
0 1
-5 4
-2 3
6 -5
-4 5
181 -262
76 -118
0 0
-7 18
-58 104
-5 6
-6 12
-3 4
1 0
11 -10
-86 130
-3 6
153 -236
-183 270
-33 64
 5
0 -1
0 -2
0 -3
0 -4
0 -5
 10
0 1
-1 -1
1 1
-1 0
1 -1
-2 -1
-2 2
-2 0
0 -2
0 -1
 20
-1 18
-2 5
-5 4
2 -33
9 -18
0 0
11 -22
2 0
-1 2
-4 41
1 6
1 -2
6 -12
0 1
-3 6
3 -6
3 -8
-1 4
2 -5
1 0
 10
2 1
-1 0
-2 -1
-1 1
0 2
2 -2
0 0
-2 -2
0 -2
-2 1
 20
-3 -3
0 4
-3 1
1 1
-1 2
-4 4
3 -1
-3 0
0 2
4 0
2 3
2 4
4 -3
-4 3
-1 1
1 3
-2 4
1 -2
1 -1
3 0
 3
0 0
0 -1
0 1
 10
2 1
-1 1
0 0
-3 1
-2 -3
-1 -2
-1 -1
1 2
3 -2
0 -2
 3
3 3
1 2
1 1
 4
0 0
1 0
2 0
3 0
 9
1 1
1 0
0 1
0 0
-1 0
-1 1
-1 -1
1 -1
0 -1
 7
1 1
-1 -1
1 0
0 1
-1 0
0 -1
0 0

4
 57
 4
 5
 21
 4
 10
 1
 1
 0
 2
 8
 3

#include <windows.h>
#include <stdio.h>
#include <iostream>
#include <math.h>

using namespace std;

typedef pair<int,int> Point;

int main()
{
   int n;
   Point* pts = 0;
   int count = 0;
   cin >> n;
   pts = new Point[n+5];
   
   for(int i=0;i < n;i++)
     cin >> pts[i].first >> pts[i].second;
     
   for(int i = 0;i < n-1;i++)
     for(int j = i + 1;j < n;j++)
     {
         for(int k = 0;k < n;k++)
         {
            if(k == i || k == j)continue;
            
            double d1 = (pts[j].first - pts[i].first);
            double d2 = (pts[j].second- pts[i].second);
            
            
            double t1 = 0.5;
            double t2 = 0.5;
            
            if(d1 != 0.0)t1 = (pts[k].first  - pts[i].first )/d1;
            if(d2 != 0.0)t2 = (pts[k].second - pts[i].second)/d2;
            
            if(t1 >= 0.0 && t1 <= 1.0 && t2 >= 0.0 && t2 <= 1.0)
            {
               count++;
               break;
            }
         }
     }
     
   cout << count;
     
   return 0;
}