#include <bits/stdc++.h>
using namespace std;
double x[(int)2e3 + 5], y[(int)2e3 + 5];
int fio() {
  int val = 0;
  char ch = getchar();
  while (ch == ' ' || ch == '\n') ch = getchar();
  while (ch >= '0' && ch <= '9') {
    val = val * 10 + ch - '0';
    ch = getchar();
  }
  return val;
}
int main() {
  int n, ans = 0;
  n = fio();
  for (int i = 0; i < n; i++) {
    x[i] = fio(), y[i] = fio();
  }
  map<pair<double, double>, int> mid_points;
  for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
      double mid_x = (x[i] + x[j]) / 2;
      double mid_y = (y[i] + y[j]) / 2;
      mid_points[make_pair(mid_x, mid_y)]++;
    }
  }
  map<pair<double, double>, int>::iterator it = mid_points.begin();
  while (it != mid_points.end()) {
    ans += it->second * (it->second - 1) / 2;
    it++;
  }
  printf("%d\n", ans);
  return 0;
}
