#include<cstdio>

using namespace std;

int modul(int p)
{if (p>0) return p;
return -p;
}


int main()
{ FILE *f=fopen("trapez.in","r");
FILE *g=fopen("trapez.out","w");
int n,i,j,x,y,r,a[2][101],b[101][101];
fscanf(f,"%d",&n);
for (i=0;i<=100;i++)
	a[0][i]=a[1][i]=0;
for (j=0;j<=100;j++)
	for (i=0;i<=100;i++)
		b[i][j]=0;
for (i=1;i<=n;i++)
  fscanf(f,"%d %d",&a[0][i],&a[1][i]);
//quicksort(1,n);
for (i=1;i<n;i++)
	for (j=i+1;j<=n;j++)
		{x=modul(a[0][i]-a[0][j]);
		y=modul(a[1][i]-a[1][j]);
		b[x][y]++;
		}
		r=0;
for (i=1;i<=100;i++)
	for (j=1;j<=100;j++)
		if (b[i][j]>1) r++;

fprintf(g,"%d",r);
		fclose(f);
		fclose(g);
		return 0;
}