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 <cstdlib>
#include <iostream>
#include <stack>
#include <cstring>
#include <cmath>
#include <string>
#include <stdio.h>
#include <map>
#include <queue>
#include <list>
#include <vector>
#include <algorithm>

#define EPS 1e-3

const long MAX=1000;

typedef __int64 LONG;

using namespace std;

struct point
{
    int x;
    int y;
};

int main(int argc, char *argv[])
{
    int n,Sum=0;
    point m[3001];
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    cin>>n;
    for(int i=0;i<n;i++) cin>>m[i].x>>m[i].y;
    for(int i=0;i<n-1;i++)
    {
        for(int j=0;j<n-1-i;j++)
        {
            if(m[j+1].x<m[j].x)
            {
                point t=m[j+1];
                m[j+1]=m[j];
                m[j]=t;
            }
        }
    }    
    for(int i=0;i<n;i++)
    {
        for(int j=i+1;j<n;j++)
        {
            double a=(double)(m[i].x+m[j].x)/2;
            double b=(double)(m[i].y+m[j].y)/2;
            int r=n-1;
            int l=0;
            int ind=-1;
            while(l<r)
            {
                int mid=(r+l)/2;
                if(m[mid].x==a)
                {
                    ind=mid;
                    l=r+1;
                }
                else if(m[mid].x>a) r=mid-1;
                else l=mid+1;
            }
            if(ind>=0)
            {
                int k=ind;
                while(k>=0 && (double)m[k].x==a && (double)m[k].y==b)
                {
                    Sum++;
                    k--;
                }
                k=ind+1;
                while(k<n && (double)m[k].x==a && (double)m[k].y==b)
                {
                    Sum++;
                    k++;
                }
            }
        }
    }
    cout<<Sum;
    //system("PAUSE");
    return EXIT_SUCCESS;
}

