#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")

inline int sig(Int r) { return (r < 0) ? -1 : (r > 0) ? +1 : 0; }
inline Int sq(Int r) { return r * r; }
struct Pt {
  Int x, y;
  Pt() : x(0), y(0) {}
  Pt(Int x_, Int y_) : x(x_), y(y_) {}
  Pt operator+(const Pt &a) const { return Pt(x + a.x, y + a.y); }
  Pt operator-(const Pt &a) const { return Pt(x - a.x, y - a.y); }
  Pt operator*(const Pt &a) const { return Pt(x * a.x - y * a.y, x * a.y + y * a.x); }
  Pt operator+() const { return Pt(+x, +y); }
  Pt operator-() const { return Pt(-x, -y); }
  Pt operator*(const Int &k) const { return Pt(x * k, y * k); }
  Pt operator/(const Int &k) const { return Pt(x / k, y / k); }
  friend Pt operator*(const Int &k, const Pt &a) { return Pt(k * a.x, k * a.y); }
  Pt &operator+=(const Pt &a) { x += a.x; y += a.y; return *this; }
  Pt &operator-=(const Pt &a) { x -= a.x; y -= a.y; return *this; }
  Pt &operator*=(const Pt &a) { return *this = *this * a; }
  Pt &operator*=(const Int &k) { x *= k; y *= k; return *this; }
  Pt &operator/=(const Int &k) { x /= k; y /= k; return *this; }
  Int abs2() const { return x * x + y * y; }
  Int dot(const Pt &a) const { return x * a.x + y * a.y; }
  Int det(const Pt &a) const { return x * a.y - y * a.x; }
  bool operator==(const Pt &a) const { return (x == a.x && y == a.y); }
  bool operator!=(const Pt &a) const { return !(x == a.x && y == a.y); }
  bool operator<(const Pt &a) const { return ((x != a.x) ? (x < a.x) : (y < a.y)); }
  friend ostream &operator<<(ostream &os, const Pt &a) { os << "(" << a.x << ", " << a.y << ")"; return os; }
};
inline Int tri(const Pt &a, const Pt &b, const Pt &c) { return (b - a).det(c - a); }

bool iSSStrict(const Pt &a, const Pt &b, const Pt &c, const Pt &d) {
  return (sig(tri(a, b, c)) * sig(tri(a, b, d)) < 0 && sig(tri(c, d, a)) * sig(tri(c, d, b)) < 0);
}


bool check(const Pt &a, const Pt &b, const Pt &c) {
  int s = sig((b - a).det(c - a));
  if (s != 0) return false;
  if (sig((b - a).dot(c - a)) <= 0) return false; // c-a-b
  if (sig((a - b).dot(c - b)) <= 0) return false; //   a-b-c
  return true;
}

int N;
vector<Pt> P;

int mod(int u) {
  return ((u %= N) < 0) ? (u + N) : u;
}

int solve() {
  for (int u = 0; u < N; ++u) for (int v = u + 1; v < N; ++v) {
    const Pt a = P[u], b = P[mod(u + 1)];
    const Pt c = P[v], d = P[mod(v + 1)];
    if (check(a, b, c)) return 0;
    if (check(a, b, d)) return 0;
    if (check(c, d, a)) return 0;
    if (check(c, d, b)) return 0;
    if (iSSStrict(a, b, c, d)) return 0;
  }
  for (int u = 0; u < N; ++u) {
    if (tri(P[u], P[mod(u + 1)], P[mod(u + 2)]) == 0) return 0;
  }
  
  __int128 area = 0;
  for (int u = 0; u < N; ++u) area += P[u].det(P[mod(u + 1)]);
  if (area < 0) reverse(P.begin(), P.end());
  for (int u = 0; u < N; ++u) {
    bool ok = true;
    for (int i = 1; i <= N - 2; ++i) {
      const int v = mod(u + i);
      const int w = mod(u + i + 1);
      ok = ok && (tri(P[u], P[v], P[w]) >= 0);
    }
    if (ok) return 1;
  }
  return -1;
}

int main() {
  for (; ~scanf("%d", &N); ) {
    P.resize(N);
    for (int u = 0; u < N; ++u) {
      scanf("%lld%lld", &P[u].x, &P[u].y);
    }
    
    const int ans = solve();
    printf("%d\n", ans);
  }
  return 0;
}