#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
bool cmp(const int &a, const int &b) {
return is_clockwise(1, a, b) == false;
}
vector <int> convexHull(vector <int> cand) {
vector <int> hull;
for(auto x : cand) {
while(hull.size() >= 2 and is_clockwise(hull[hull.size() - 2], hull.back(), x) == true) {
hull.pop_back();
}
hull.push_back(x);
}
return hull;
}
int main() {
int N = get_n();
vector <int> L, R;
for(int i = 3; i <= N; i++) {
if(is_clockwise(1, 2, i) == true) {
L.push_back(i);
}
else {
R.push_back(i);
}
}
sort(L.begin(), L.end(), cmp);
sort(R.begin(), R.end(), cmp);
L.push_back(2);
R.push_back(1);
L = convexHull(L), R = convexHull(R);
vector <int> res;
for(auto x : L) {
res.push_back(x);
}
for(auto x : R) {
res.push_back(x);
}
res = convexHull(res);
deque <int> hull(res.begin(), res.end());
bool ok = true;
while(ok == true) {
ok = false;
int x = hull.back();
hull.pop_back();
if(is_clockwise(hull.back(), x, hull.front()) == true) {
ok = true;
}
else {
hull.push_back(x);
}
x = hull.front();
hull.pop_front();
if(is_clockwise(hull.front(), x, hull.back()) == false) {
ok = true;
}
else {
hull.push_front(x);
}
}
give_answer(hull.size());
}
