#include<bits/stdc++.h>
#include "trilib.h"
#define pb push_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
using namespace std;
using ll = long long;
using vi = vector<int>;
const int mod = 1e9 + 7;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
namespace local {
int p = -1;
using vec = complex<int>;
int cross(vec a, vec b) {
return (conj(a)*b).imag();
}
vector<vec> v;
int N;
int get_n() {
cin >> N;
// N = 20;
v.resize(N);
for(auto &i : v) {
int x, y;
cin >> x >> y;
// x = rng()%100, y = rng()%100;
i = vec(x, y);
}
return N;
}
void give_answer(int x) {
if(p!=-1&&p!=x) {
cout << "WA\n";
cout << N << "\n";
for(auto i : v)
cout << i.real() << " " << i.imag() << "\n";
}
cout << "ANSWER:" << x << "\n";
p=x;
}
bool is_clockwise(int a, int b, int c) {
// cerr << a << " " << b << " " << c << "\n";
if(a!=b&&b!=c&&c!=a)
assert(cross(v[b-1]-v[a-1], v[c-1]-v[a-1]));
return cross(v[b-1]-v[a-1], v[c-1]-v[a-1])>0;
}
}
// using namespace local;
int n;
int check(int a) {
int b = 1+(a==1);
for(int i = 1; i <= n; i++)
if(i!=a&&i!=b&&is_clockwise(a, b, i))
b = i;
for(int i = 1; i <= n; i++)
if(i!=a&&i!=b&&is_clockwise(a, b, i))
return 0;
return 1;
}
vi hull(vi v, int V) {
sort(all(v), [&](const int& a, const int &b) {
return !is_clockwise(V, a, b);
});
vi hull = {V};
for(auto i : v) {
while(hull.size()>1&&is_clockwise(hull[hull.size()-2], hull.back(), i))
hull.pop_back();
hull.pb(i);
}
return hull;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
n = get_n();
vi a[2];
a[0].pb(2);
for(int i = 3; i <= n; i++) a[is_clockwise(1, 2, i)].pb(i);
vi x = hull(a[0], 1), y = hull(a[1], 1);
#define a x
#define b y
reverse(all(y));//0 = top, 1 = bottom
while(a.size()&&b.size()) {
if(a.size()==1&&b.size()==1) break;
int A = a.size(), B = b.size();
if(A>1&&is_clockwise(a[A-2], a[A-1], b[B-1])) {
a.pop_back();
}else
if(B>1&&is_clockwise(a[A-1], b[B-1], b[B-2])) {
b.pop_back();
} else break;
}
reverse(all(x)), reverse(all(y));
while(a.size()&&b.size()) {
if(a.size()==1&&b.size()==1) break;
int A = a.size(), B = b.size();
if(A>1&&!is_clockwise(a[A-2], a[A-1], b[B-1])) {
a.pop_back();
}else
if(B>1&&!is_clockwise(a[A-1], b[B-1], b[B-2])) {
b.pop_back();
}else break;
}
give_answer(a.size()+b.size());
}
