#include <stdio.h>
#include <limits.h>
#include <stdlib.h>
#include <algorithm>
using namespace std;
int main()
{int n,a[1005],b[1005],i,nr,j;
 long long p[1000009],k=0;
 
 freopen("trapez.in","r",stdin);
 freopen("trapez.out","w",stdout);
 scanf("%d",&n);
 for (i=1;i<=n;i++)
	 {scanf("%d %d",&a[i],&b[i]);
  for (j=1;j<=i-1;j++) 
   {nr++;
    p[nr]=abs(a[i]-a[j]);
	p[nr]*=INT_MAX;
	p[nr]+=abs(b[i]-b[j]);}
 }
 sort(p+1,p+nr+1);
 for (i=1;i<=nr;)
  {for (j=i+1;j<=nr+1;j++)
	  if (p[i]!=p[j]) break;
   k+=(j-1-i)*(j-i)/2;
   i=j;
  }
  printf("%lld",k);
return 0;}