#include "trilib.h"
#include<bits/stdc++.h>
#define eb emplace_back
#define iter(a) a.begin(), a.end()
#define lsort(a) sort(iter(a))
#define uni(a) a.resize(unique(iter(a)) - a.begin())
#define printv(a, b) {\
for(auto pv : a) b << pv << " ";\
b << "\n";\
}
#define mt make_tuple
#define mp make_pair
#define F first
#define S second
using namespace std;
typedef long long ll;
using tiii = tuple<int, int, int>;
using pii = pair<int, int>;
void waassert(bool b){
if(b) return;
cout << "OAO\n";
exit(0);
}
int n;
vector<int> hull;
map<tiii, int> qry;
int query(int a, int b, int c){
if(qry.find(mt(a, b, c)) != qry.end()) return qry[mt(a,b,c)];
//waassert(a != b && b != c && c != a);
return is_clockwise(a, b, c);
}
bool check0(int id, int i){
int m = hull.size();
int lst = (i - 1 + m) % m;
int nxt = (i + 1) % m;
return query(id, hull[lst], hull[i]) || query(id, hull[i], hull[nxt]);
}
bool check(int id, int i){
int m = hull.size();
int lst = (i - 1 + m) % m;
int nxt = (i + 1) % m;
return query(id, hull[lst], hull[i]) && query(id, hull[i], hull[nxt]);
}
void add(int id){
//cerr << "test " << id << "\n";
int m = hull.size();
int l = 0, r = m - 1;
while(l < r){
int mid = (l + r + 1) / 2;
if(query(id, hull[0], hull[mid]) == query(id, hull[0], hull[1])) l = mid;
else r = mid - 1;
}
deque<int> a, b;
for(int i = 0; i <= l; i++) a.eb(i);
for(int i = l + 1; i < m; i++) b.eb(i);
vector<vector<int>> del(4);
while(!a.empty() && check0(id, a.front())){
if(!check(id, a.front())) del[0].eb(a.front());
a.pop_front();
}
while(!a.empty() && check0(id, a.back())){
if(!check(id, a.back())) del[1].eb(a.back());
a.pop_back();
}
while(!b.empty() && check0(id, b.front())){
if(!check(id, b.front())) del[2].eb(b.front());
b.pop_front();
}
while(!b.empty() && check0(id, b.back())){
if(!check(id, b.back())) del[3].eb(b.back());
b.pop_back();
}
/*cerr << "A ";
printv(a, cerr);
cerr << "B ";
printv(b, cerr);
for(int i = 0; i < 4; i++){
cerr << "D" << i << " ";
printv(del[i], cerr);
}*/
vector<int> tmp;
tmp.swap(hull);
bool ok1 = false, ok2 = false;
auto put = [&](int i){
if(ok1 && ok2) hull.eb(id);
hull.eb(tmp[i]);
if(ok1 && !ok2) hull.eb(id);
ok1 = true;
ok2 = true;
};
for(int i : del[0]) put(i);
for(int i : a) hull.eb(tmp[i]), ok2 = false;
for(int i : del[1]) put(i);
for(int i : del[2]) put(i);
for(int i : b) hull.eb(tmp[i]), ok2 = false;
for(int i : del[3]) put(i);
if(hull.size() == 3 && query(hull[0], hull[1], hull[2])){
reverse(iter(hull));
}
//printv(hull, cerr);
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
n = get_n();
if(query(1, 2, 3)){
hull = {3, 2, 1};
}
else{
hull = {1, 2, 3};
}
for(int i = 4; i <= n; i++) add(i);
give_answer(hull.size());
return 0;
}
