#include <bits/stdc++.h>
using namespace std;
inline bool EQ(double a, double b) { return fabs(a - b) < 1e-9; }
inline bool isLeapYear(long long int year) {
  return (year % 400 == 0) | (year % 4 == 0 && year % 100 != 0);
}
inline void normal(long long int &a) {
  a %= 1000000007;
  (a < 0) && (a += 1000000007);
}
inline long long int modMul(long long int a, long long int b) {
  a %= 1000000007, b %= 1000000007;
  normal(a), normal(b);
  return (a * b) % 1000000007;
}
inline long long int modAdd(long long int a, long long int b) {
  a %= 1000000007, b %= 1000000007;
  normal(a), normal(b);
  return (a + b) % 1000000007;
}
inline long long int modSub(long long int a, long long int b) {
  a %= 1000000007, b %= 1000000007;
  normal(a), normal(b);
  a -= b;
  normal(a);
  return a;
}
inline long long int modPow(long long int b, long long int p) {
  long long int r = 1;
  while (p) {
    if (p & 1) r = modMul(r, b);
    b = modMul(b, b);
    p >>= 1;
  }
  return r;
}
inline long long int modInverse(long long int a) {
  return modPow(a, 1000000007 - 2);
}
inline long long int modDiv(long long int a, long long int b) {
  return modMul(a, modInverse(b));
}
inline bool isInside(pair<int, int> p, long long int n, long long int m) {
  return (p.first >= 0 && p.first < n && p.second >= 0 && p.second < m);
}
inline bool isInside(pair<int, int> p, long long int n) {
  return (p.first >= 0 && p.first < n && p.second >= 0 && p.second < n);
}
inline bool isSquare(long long int x) {
  long long int s = sqrt(x);
  return (s * s == x);
}
inline bool isFib(long long int x) {
  return isSquare(5 * x * x + 4) || isSquare(5 * x * x - 4);
}
inline bool isPowerOfTwo(long long int x) {
  return ((1LL << (long long int)log2(x)) == x);
}
struct func {
  bool operator()(pair<int, int> const &a, pair<int, int> const &b) {
    if (a.first == b.first) return (a.second < b.second);
    return (a.first < b.first);
  }
};
const long long int INF = 0x3f3f3f3f3f3f3f3f;
const long double EPS = 1e-9;
const int inf = 0x3f3f3f3f;
const int mx = (int)1e5 + 9;
struct Point {
  long long int s, p, x, y;
  string name;
  bool operator<(const Point &ob) const {
    return s == ob.s ? p < ob.p : s > ob.s;
  }
};
double distance(Point a, Point b) {
  return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
long long int n, m, t, i, j, res;
long long int counT(long long int x[], long long int y[], int N) {
  map<pair<long long int, long long int>, long long int> mp;
  for (int i = 0; i < N; i++) {
    for (int j = i + 1; j < N; j++) {
      long long int midX = x[i] + x[j];
      long long int midY = y[i] + y[j];
      mp[{midX, midY}]++;
    }
  }
  res = 0;
  for (auto it : mp) {
    long long int freq = it.second;
    res += freq * (freq - 1) / 2;
  }
  return res;
}
int main() {
  scanf("%lld", &t);
  long long int arr[t + 9], brr[t + 9];
  for (int i = 0; i < (t); i++) {
    scanf("%lld", &arr[i]);
    scanf("%lld", &brr[i]);
  }
  printf("%lld\n", counT(arr, brr, t));
}
