399

#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstring>
#define X first
#define Y second
using namespace std;

int main() {
    pair<int,int> pt[1005]={};
    int N,x,y;
    vector<long long> len;
    len.clear();
    cin >> N;
    for(int i = 0;i < N;i++){
        cin >> x >> y;
        pt[i] = make_pair(x , y);
    }
    for(int i = 0;i < N;i++)for(int j = i + 1;j < N;j++){
        len.push_back(pow(pt[j].X-pt[i].X,2) + pow(pt[j].Y-pt[i].Y,2));
    }

    sort(len.begin(), len.end());
    long long tmp = len[0];
    int ans = 0, count = 1;
    for(int i = 1;i < len.size();i++){
        if(len[i] == tmp)count++;
        else{
            //cout << "count " << count << endl;
            tmp = len[i];
            ans+=(count*(count-1)/2);
            count = 1;
        }
    }
    ans+=(count*(count-1)/2);
    cout << ans << endl;
    return 0;
}