#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=long double;
const ll ILL=2167167167167167167;
const int INF=2100000000;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> int LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> int UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(b<a){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;}
template<class T> void vec_out(vector<T> &p,int ty=0){
    if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
    else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}

struct point{
    ll x;
    ll y;
};


void solve();
// CITRUS CURIO CITY / FREDERIC
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    // cin >> t;
    rep(i, 0, t) solve();
}

void solve(){
    int N;
    cin >> N;
    vector<point> p(N);
    rep(i, 0, N){
        cin >> p[i].x >> p[i].y;
    }
    rep(i, 0, N) p.push_back(p[i]);
    auto f = [&](point a, point b, point c) -> int {
        ll A = a.y - b.y;
        ll B = b.x - a.x;
        ll C = -(A * a.x + B * a.y);
        assert(A * b.x + B * b.y + C == 0);
        ll res = A * c.x + B * c.y + C;
        if (res < 0) return -1;
        if (res > 0) return 1;
        return 0;
    };
    rep(i, 0, N){
        // 同一直線上
        if (f(p[i], p[i + 1], p[i + 2]) == 0){
            cout << "0\n";
            return;
        }
        // 自己交差
        rep(j, 2, N - 1){
            int a = f(p[i], p[i + 1], p[i + j]);
            int b = f(p[i], p[i + 1], p[i + j + 1]);
            int c = f(p[i + j], p[i + j + 1], p[i]);
            int d = f(p[i + j], p[i + j + 1], p[i + 1]);
            if (a != b && c != d){
                cout << "0\n";
                return;
            }
        }
    }
    // Yes
    rep(rp, 0, 2){
        reverse(all(p));
        rep(i, 0, N){
            rep(j, 0, N) if (i != j){
                p[j].x -= p[i].x;
                p[j].y -= p[i].y;
            }
            p[i].x = 0, p[i].y = 0;
            vector<int> order;
            rep(j, 0, N) if (j != i) order.push_back(j);
            sort(all(order), [&](int l, int r){
               if (l == r) return false;
               if (p[l].y == 0 && p[r].y == 0){
                   if ((p[l].x > 0) ^ (p[r].x > 0)){
                       return p[l].x > 0;
                   }
                   return p[l].x < p[r].x;
               }
               if (p[l].y == 0){
                   return p[l].x > 0 || p[r].y < 0;
               }
               if (p[r].y == 0){
                   return p[r].x < 0 && p[l].y > 0;
               }
               if ((p[l].y < 0) ^ (p[r].y < 0)){
                   return p[l].y > 0;
               }
               return p[l].x * p[r].y > p[l].y * p[r].x;
            });
            rep(j, 0, N - 1) order.push_back(order[j]);
            rep(j, 0, N - 1) if (order[j] == (i + 1) % N){
                bool ok = true;
                rep(k, 1, N){
                    if (order[j + k - 1] != (i + k) % N) ok = false;
                }
                if (ok){
                    cout << "1\n";
                    return;
                }
            }
        }
    }
    // No
    cout << "-1\n";
}