#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const ll MAXN = 40001;
int N, p, q;
vector<int> A, B;
list<int> C;
list<int>::iterator bef(list<int>::iterator t)
{
if(t!=C.begin()) return prev(t);
else return prev(C.end());
}
list<int>::iterator nxt(list<int>::iterator t)
{
if(t==prev(C.end())) return C.begin();
else return next(t);
}
int cnt=0;
bool ccw(int a, int b, int c)
{
bool t=is_clockwise(a, b, c);
return !t;
}
int main()
{
int i, j;
N=get_n();
for(i=3; i<=N; i++)
{
if(ccw(1, 2, i)) A.push_back(i);
else B.push_back(i);
}
A.push_back(2); B.push_back(2);
stable_sort(A.begin(), A.end(), [&](const int &p, const int &q) { return ccw(1, p, q); });
stable_sort(B.begin(), B.end(), [&](const int &p, const int &q) { return !ccw(1, p, q); });
A.insert(A.begin(), 1);
B.insert(B.begin(), 1);
vector<int> S;
for(auto it : A)
{
while(S.size()>1 && !ccw(S[S.size()-2], S[S.size()-1], it)) S.pop_back();
S.push_back(it);
}
A=S; S.clear();
for(auto it : B)
{
while(S.size()>1 && ccw(S[S.size()-2], S[S.size()-1], it)) S.pop_back();
S.push_back(it);
}
B=S; S.clear();
A.erase(A.begin()); A.erase(A.begin());
B.erase(B.begin()); B.erase(B.begin());
reverse(B.begin(), B.end());
queue<list<int>::iterator> Q;
C.push_back(1);
for(auto it : B) C.push_back(it);
C.push_back(2);
for(auto it : A) C.push_back(it);
set<int> vis;
for(auto it=C.begin(); it!=C.end(); it++) if(!ccw(*bef(it), *it, *nxt(it))) Q.push(it), vis.insert(*it);
while(!Q.empty() && C.size()>3)
{
auto now=Q.front(); Q.pop();
auto l=bef(now), r=nxt(now);
C.erase(now);
if(vis.find(*l)==vis.end() && !ccw(*bef(l), *l, *nxt(l))) Q.push(l), vis.insert(*l);
if(vis.find(*r)==vis.end() && !ccw(*bef(r), *r, *nxt(r))) Q.push(r), vis.insert(*r);
}
give_answer(C.size());
}
