#include <bits/stdc++.h>
#include "trilib.h"
#define lli long long int
#define ld long double
#define pb push_back
#define MP make_pair
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define REP(i, n) for(int i = 0; (i) < (n); (i)++)
using namespace std;
void fastio() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
}
int n;
void find_hull(vector<int> &p, vector<int> &hull) {
if(p.size() < 3) return;
int piv = p[0];
p.erase(p.begin());
auto comp = [&piv](int x, int y) {
return is_clockwise(piv, x, y);
};
sort(all(p), comp);
hull.clear();
hull.pb(piv);
hull.pb(p[0]);
for(int i = 2; i < p.size(); i++) {
while(hull.size() > 1 && !is_clockwise(hull[hull.size() - 2], hull.back(), p[i])) {
hull.pop_back();
}
hull.pb(p[i]);
}
}
void solve() {
n = get_n();
vector<int> p;
for(int i = 1; i <= n; i++) {
p.pb(i);
}
vector<int> pl = {2, 1}, pr = {1, 2};
for(int i = 3; i <= n; i++) {
if(is_clockwise(1, 2, i)) {
pl.pb(i);
}
else {
pr.pb(i);
}
}
vector<int> hull1, hull2;
find_hull(pl, hull1);
find_hull(pr, hull2);
// hull1 starts with 2, hull2 starts with 1
// cout << "hull1: ";
// for(auto c : hull1) {
// cout << c << " ";
// }
// cout << "\nhull2: ";
// for(auto c : hull2) {
// cout << c << " ";
// }
// cout << "\n";
hull1.pop_back(); hull2.pop_back();
reverse(all(hull1));
while(1) {
if(hull1.size() > 1 && hull2.size() && !is_clockwise(hull2.back(), hull1.back(), hull1[hull1.size() - 2])) {
hull1.pop_back();
continue;
}
if(hull2.size() > 1 && hull1.size() && !is_clockwise(hull2[hull2.size() - 2], hull2.back(), hull1.back())) {
hull2.pop_back();
continue;
}
break;
}
reverse(all(hull1));
reverse(all(hull2));
while(1) {
if(hull1.size() > 1 && hull2.size() && is_clockwise(hull2.back(), hull1.back(), hull1[hull1.size() - 2])) {
hull1.pop_back();
continue;
}
if(hull2.size() > 1 && hull1.size() && is_clockwise(hull2[hull2.size() - 2], hull2.back(), hull1.back())) {
hull2.pop_back();
continue;
}
break;
}
for(auto c : hull2) {
hull1.pb(c);
}
sort(all(hull1));
hull1.resize(unique(all(hull1)) - hull1.begin());
give_answer(hull1.size());
}
signed main() {
solve();
}
