#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

struct Vec {
  using etype = int;  // type of elements
  using ptype = int;  // type of product results
  etype x = 0, y = 0;
  constexpr Vec operator-() const { return {-x, -y}; }
  friend constexpr Vec operator+(const Vec& a, const Vec& b) { return {a.x + b.x, a.y + b.y}; }
  friend constexpr Vec operator-(const Vec& a, const Vec& b) { return {a.x - b.x, a.y - b.y}; }
  friend constexpr ptype operator*(const Vec& a, const Vec& b) { return (ptype)a.x * b.y - (ptype)a.y * b.x; }
  template <class T, enable_if_t<is_integral_v<T>>* = nullptr>
  friend constexpr Vec operator*(T c, const Vec& a) { return {c * a.x, c * a.y}; }
  template <class T, enable_if_t<is_integral_v<T>>* = nullptr>
  friend constexpr Vec operator*(const Vec& a, T c) { return c * a; }
  template <class T, enable_if_t<is_integral_v<T>>* = nullptr>
  friend constexpr Vec operator/(const Vec& a, T c) { return {a.x / c, a.y / c}; }
  Vec& operator+=(const Vec& a) { x += a.x; y += a.y; return *this; }
  Vec& operator-=(const Vec& a) { x -= a.x; y -= a.y; return *this; }
  template <class T, enable_if_t<is_integral_v<T>>* = nullptr>
  Vec& operator*=(T c) { x *= c; y *= c; return *this; }
  friend constexpr bool operator==(const Vec& a, const Vec& b) { return a.x == b.x && a.y == b.y; }
  friend constexpr bool operator!=(const Vec& a, const Vec& b) { return !(a == b); }
  constexpr int quadrant() const { return y > 0 ? (x > 0 ? 0 : 1) : y < 0 ? (x < 0 ? 2 : 3) : (x > 0 ? 0 : x < 0 ? 2 : -1); }
  friend constexpr bool operator<(const Vec& a, const Vec& b) {
    int qa = a.quadrant(), qb = b.quadrant();
    if (qa != qb) return qa < qb;
    ptype p1 = (ptype)a.x * b.y, p2 = (ptype)a.y * b.x;
    return p1 > p2 || (p1 == p2 && (a.x != 0 ? abs(a.x) < abs(b.x) : abs(a.y) < abs(b.y)));
  }
  friend constexpr bool operator>(const Vec& a, const Vec& b) { return b < a; }
  friend constexpr bool operator<=(const Vec& a, const Vec& b) { return !(b < a); }
  friend constexpr bool operator>=(const Vec& a, const Vec& b) { return !(a < b); }
  constexpr int ccw(const Vec& u, const Vec& v) const { ptype p = (u - *this) * (v - *this); return p > 0 ? 1 : p < 0 ? -1 : 0; }
  static constexpr bool intersects(const Vec& a, const Vec& b, const Vec& c, const Vec& d) { return a.ccw(b, c) * a.ccw(b, d) <= 0 && c.ccw(d, a) * c.ccw(d, b) <= 0; }
  constexpr bool parallel_to(const Vec& a) const { return (ptype)x * a.y == (ptype)y * a.x; }
  constexpr ptype dot(const Vec& a) const { return (ptype)x * a.x + (ptype)y * a.y; }
  constexpr ptype norm2() const { return (ptype)x * x + (ptype)y * y; }
  constexpr bool is_zero() const { return x == 0 && y == 0; }
  constexpr Vec normalize() const {
    if (x == 0) return Vec{0, (y == 0 ? 0 : 1)};
    etype g = gcd(x, y);
    return *this / (x > 0 ? g : -g);
  }
  constexpr Vec rot90() const { return {-y, x}; }
  // exclusive
  constexpr bool in_between(const Vec& a, const Vec& b) const {
    Vec x = a - *this, y = b - *this;
    return x.parallel_to(y) && x.dot(y) < 0;
  }
  friend std::ostream& operator<< (std::ostream& os, const Vec& t) { return os << t.x << ' ' << t.y; }
  friend std::istream& operator>> (std::istream& os, Vec& t) { return os >> t.x >> t.y; }
};

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  vector<Vec> p(n);
  rep(i, n) cin >> p[i];
  if (n == 1) {
    cout << 1 << '\n';
    return 0;
  }
  Vec pp[12][12];
  rep(i, n) rep(j, n) pp[i][j] = p[j] - p[i];
  bool straight[12][12][12];
  rep(i, n) rep(j, n) rep(k, n) straight[i][j][k] = p[j].in_between(p[i], p[k]);
  int cross[12][12][12][12];
  rep(i, n) rep(j, n) rep(k, n) rep(l, n) cross[i][j][k][l] = pp[i][j] * pp[k][l];
  int dp[1 << 12][12][12];
  constexpr int INF = 1001001001;
  rep(i, 1 << 12) rep(j, 12) rep(k, 12) dp[i][j][k] = INF;
  rep(i, n) rep(j, n) if (i != j) dp[1 << i | 1 << j][i][j] = 2;
  rep(s, 1 << n) rep(i, n) rep(j, n) if (int v = dp[s][i][j]; v < INF) {
    rep(k, n) if (!(s >> k & 1)) {
      chmin(dp[s | 1 << k][j][k], v + !straight[i][j][k]);
    }
    rep(k, n) if (!(s >> k & 1)) rep(l, n) if (k != l && !(s >> l & 1)) {
      if (cross[j][i][k][l] > 0 && cross[j][i][j][k] > 0 && cross[k][l][k][j] < 0 ||
          cross[j][i][k][l] < 0 && cross[j][i][j][k] < 0 && cross[k][l][k][j] > 0) {
        chmin(dp[s | 1 << k | 1 << l][k][l], v + 1);
      }
    }
  }
  int ans = INF;
  rep(i, n) rep(j, n) chmin(ans, dp[(1 << n) - 1][i][j]);
  cout << ans - 1 << '\n';
}