#include <bits/stdc++.h>

#include <atcoder/all>

using namespace std;
using namespace atcoder;

struct Fast {
  Fast() {
    std::cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << setprecision(10);
  }
} fast;

#define popcount(x) __builtin_popcount(x)
#define all(a) (a).begin(), (a).end()
#define contains(a, x) ((a).find(x) != (a).end())
#define rep(i, a, b) for (int i = (a); i < (int)(b); i++)
#define rrep(i, a, b) for (int i = (int)(b)-1; i >= (a); i--)
#define YN(b) cout << ((b) ? "YES" : "NO") << "\n";
#define Yn(b) cout << ((b) ? "Yes" : "No") << "\n";
#define yn(b) cout << ((b) ? "yes" : "no") << "\n";

using ll = long long;

template <typename T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

int main() {
  using lll = __int128_t;
  using P = pair<lll, lll>;

  auto Area = [&](P p) {
    if (p.first > 0 && p.second >= 0) return 0;
    if (p.first <= 0 && p.second > 0) return 1;
    if (p.first < 0 && p.second <= 0) return 2;
    if (p.first >= 0 && p.second < 0) return 3;
    return -1;
  };
  auto Dot = [&](P p1, P p2) {
    return p1.first * p2.first + p1.second * p2.second;
  };
  auto Cross = [&](P p1, P p2) {
    return p1.first * p2.second - p1.second * p2.first;
  };

  int n;
  cin >> n;
  vector<P> pos;
  rep(i, 0, n) {
    ll x, y;
    cin >> x >> y;
    pos.push_back(P(x, y));
  }
  int ans = 0;
  rep(i, 0, pos.size()) {
    vector<P> possub;
    rep(j, 0, pos.size()) {
      if (i != j) possub.push_back(P(pos[j].first - pos[i].first, pos[j].second - pos[i].second));
    }
    sort(all(possub), [Area, Cross](P const &p1, P const &p2) {
      if (Area(p1) != Area(p2)) return Area(p1) < Area(p2);
      return Cross(p1, p2) > 0;
    });
    for (int j = 0; j + 1 < (int)possub.size(); j++) {
      auto p1 = possub[j];
      auto p2 = possub[j + 1];
      if (Dot(p1, p2) > 0 && Cross(p1, p2) == 0) {
        ans++;
        break;
      }
    }
  }
  cout << ans << "\n";
}