#include <bits/stdc++.h>

#define ll long long
#define ld long double

using namespace std;

ifstream fin("patrate3.in");
ofstream fout("patrate3.out");

const int NMAX = 1000;
const ld INF = 1e18;
const ld EPS = 1e-8;

int n;
ll answer;
int x[NMAX + 1], y[NMAX + 1];
vector<pair<ld, ll>> v;

ld get_slope(int x1, int y1, int x2, int y2) {
    if(x2 - x1 == 0) {
        return INF;
    }
    return (ld)(y2 - y1) / (ld)(x2 - x1);
}

ll get_distance(int x1, int y1, int x2, int y2) {
    return (ll)(x2 - x1) * (x2 - x1) + (ll)(y2 - y1) * (y2 - y1);
}

bool is_equal(pair<ld, ll> a, pair<ld, ll> b) {
    if(abs(a.first - b.first) <= EPS && a.second == b.second) {
        return true;
    }
    return false;
}

int main()
{
    fin >> n;
    for(int i = 1; i <= n; i++) {
        ld xx, yy;
        fin >> xx >> yy;
        x[i] = round(xx * 10000);
        y[i] = round(yy * 10000);
    }

    for(int i = 1; i <= n; i++) {
        for(int j = i + 1; j <= n; j++) {
            ld slope = get_slope(x[i], y[i], x[j], y[j]);
            assert(slope <= INF);
            ll dist = get_distance(x[i], y[i], x[j], y[j]);
            v.emplace_back(slope, dist);
        }
    }

    sort(v.begin(), v.end());
    int l = 1;
    for(int i = 1; i < (int) v.size(); i++) {
        if(is_equal(v[i], v[i - 1])) {
            l++;
        }
        else {
            answer += (ll) l * (l - 1) / 2;
            l = 1;
        }
    }
    answer += (ll) l * (l - 1) / 2;
    fout << answer / 2 << '\n';
    return 0;
}