1 #include <iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 #include<stdlib.h> 6 #include<vector> 7 #include<cmath> 8 #include<queue> 9 #include<set>10 using namespace std;11 #define N 101012 #define mod 9999113 #define LL long long14 #define INF 0xfffffff15 const double eps = 1e-8;16 const double pi = acos(-1.0);17 const double inf = ~0u>>2;18 struct point19 {20     int x,y;21     point(int x=0,int y=0):x(x),y(y){}22 }p[N],o[N];23 int next[N],head[mod],t;24 void insert(int i)25 {26     int key = (p[i].x*p[i].x+p[i].y*p[i].y)%mod;27     next[t] = head[key];28     o[t].x = p[i].x;29     o[t].y = p[i].y;30     head[key] = t++;31 }32 int find(point a)33 {34     int  key = (a.x*a.x+a.y*a.y)%mod;35     int i;36     for(i = head[key] ; i!= -1 ; i = next[i])37     {38         if(o[i].x==a.x&&o[i].y == a.y) return 1;39     }40     return 0;41 }42 bool cmp(point a,point b)43 {44     if(a.x==b.x)45     return a.y<b.y;46     return a.x<b.x;47 }48 int main()49 {50     int n,i,j;51     while(scanf("%d",&n)&&n)52     {53         memset(head,-1,sizeof(head));54         t = 0;55         for(i = 1; i <= n; i++)56         {57             scanf("%d%d",&p[i].x,&p[i].y);58             insert(i);59         }60         //sort(p+1,p+n+1,cmp);61         int ans = 0;62         for(i = 1; i <= n ;i++)63             for(j = 1 ; j <= n; j++)64             {65                 if(i==j) continue;66                 point p1,p2;67                 p1.x = p[i].x+(p[i].y-p[j].y);68                 p1.y = p[i].y-(p[i].x-p[j].x);69                 p2.x = p[j].x+(p[i].y-p[j].y);70                 p2.y = p[j].y-(p[i].x-p[j].x);71                 if(!find(p1)) continue;72                 if(!find(p2)) continue;73                 ans++;74             }75         printf("%d\n",ans/4);76     }77     return 0;