#include <stdio.h>
#include <math.h>
#include <iostream>
#include <string>
#include <stdlib.h>
#include <assert.h>
#include <time.h>
#include <algorithm>
using namespace std;
#define NMax 1001
struct punct
{
	int x, y;
};
int compare(const void *a, const void *b)
{
	return (*(int*)a - *(int*)b);
}
int main()
{
	int n; punct p[NMax];
	FILE *f = fopen("trapez.in", "r");
	FILE *g = fopen("trapez.out", "w");
	fscanf(f, "%d", &n);
	for (int i = 0; i < n; i++)
	{
		fscanf(f, "%d %d", &p[i].x, &p[i].y);
	}
	double pante[NMax*NMax]; int k = 0;
	for (int i = 0; i < n*n; i++)
		pante[i] = 1;
	for (int i = 0; i < n-1; i++)
	{
		for (int j = i+1; j < n; j++)
		{
			int x = (p[i].x - p[j].x);
			pante[k] = (p[i].y - p[j].y) ;
			pante[k++] *= x;
		}
	}
	qsort(pante, k-1, sizeof(double), compare);
	int nr = 1, nrTrapeze = 0;
	for (int i = 0; i < k-1; i++)
	{
		if (pante[i] == pante[i+1])
			nr++;
		else
		{
			nrTrapeze += nr * (nr - 1) / 2;
			nr = 1;
		}
	}
	fprintf(g, "%d", nrTrapeze);
	fclose(f); fclose(g);
	return 0;
}