#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;

struct Node {
  int u;
  int v;
  ll dist;

  Node(int u = -1, int v = -1, ll dist = 0.0) {
    this->u = u;
    this->v = v;
    this->dist = dist;
  }

  bool operator>(const Node &n) const {
    return dist > n.dist;
  }
};

int main() {
  int N;
  cin >> N;
  vector<ll> X(N);
  vector<ll> Y(N);

  for (int i = 0; i < N; ++i) {
    cin >> X[i] >> Y[i];
  }

  priority_queue <Node, vector<Node>, greater<Node>> pque;

  for (int i = 0; i < N; ++i) {
    ll x1 = X[i];
    ll y1 = Y[i];

    for (int j = i + 1; j < N; ++j) {
      ll x2 = X[j];
      ll y2 = Y[j];
      ll dx = x1 - x2;
      ll dy = y1 - y2;
      pque.push(Node(i, j, dx * dx + dy * dy));
    }
  }

  int ans = 0;
  bool checked[N];
  memset(checked, false, sizeof(checked));

  while (!pque.empty()) {
    Node node = pque.top();
    pque.pop();

    if (checked[node.u]) continue;
    if (checked[node.v]) continue;

    if (node.u == 0) {
      ++ans;
      checked[node.v] = true;
    } else {
      checked[node.u] = true;
      checked[node.v] = true;
    }
  }

  cout << ans << endl;

  return 0;
}