CodeForces 660D. Number of Parallelograms【模拟】

D. Number of Parallelograms

time limit per test

4 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

You are given n points on a plane. All the points are distinct and no three of them lie on the same line. Find the number of parallelograms with the vertices at the given points.

Input

The first line of the input contains integer n (1 ≤ n ≤ 2000) — the number of points.

Each of the next n lines contains two integers (xi, yi) (0 ≤ xi, yi ≤ 109) — the coordinates of the i-th point.

Output

Print the only integer c — the number of parallelograms with the vertices at the given points.

Example

input

40 11 01 12 0

output

1

AC-code：

<pre name="code" class="cpp">#include<cstdio>#include<algorithm>using namespace std;struct node{int x,y;}s[2005],p[2005*2005];bool cmp(node a,node b){if(a.x==b.x)return a.y>b.y;return a.x>b.x;}int main(){int n,i,j,t,k,sum;scanf("%d",&n);for(i=0;i<n;i++)scanf("%d%d",&s[i].x,&s[i].y);sort(s,s+n,cmp);for(t=0,i=0;i<n-1;i++)for(j=i+1;j<n;j++){p[t].x=s[i].x-s[j].x;p[t++].y=s[i].y-s[j].y;}sort(p,p+t,cmp);sum=0;for(i=1,k=0;i<t;i++){if(p[i-1].x==p[i].x&&p[i].y==p[i-1].y)continue;else{sum+=(i-k-1)*(i-k)/2;k=i;}}sum+=(i-k-1)*(i-k)/2;printf("%d\n",sum/2);return 0;}