#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
//#include "temp.cpp"
// #include "B.cpp"
#include "trilib.h"
#include <cstdio>
using namespace std;
#ifndef ONLINE_JUDGE
#define dbg(x) cerr << #x <<" "; print(x); cerr << endl;
#else
#define dbg(x)
#endif
#define sz(x) (int((x).size()))
#define len(x) (int)x.length()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define clr(x) (x).clear()
#define uniq(x) x.resize(unique(all(x)) - x.begin());
#define blt(x) __builtin_popcount(x)
#define pb push_back
#define popf pop_front
#define popb pop_back
void print(long long t) {cerr << t;}
void print(int t) {cerr << t;}
void print(string t) {cerr << t;}
void print(char t) {cerr << t;}
void print(double t) {cerr << t;}
void print(long double t) {cerr << t;}
void print(unsigned long long t) {cerr << t;}
template <class T, class V> void print(pair <T, V> p);
template <class T> void print(vector <T> v);
template <class T> void print(set <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(T v[],V n) {cerr << "["; for(int i = 0; i < n; i++) {print(v[i]); cerr << " "; } cerr << "]";}
template <class T, class V> void print(pair <T, V> p) {cerr << "{"; print(p.first); cerr << ","; print(p.second); cerr << "}";}
template <class T> void print(vector <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(deque <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(set <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(multiset <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void print(map <T, V> v) {cerr << "[ "; for (auto i : v) {print(i); cerr << " ";} cerr << "]";}
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define nl '\n'
// for grid problems
int dx[8] = {-1,0,1,0,1,-1,1,-1};
int dy[8] = {0,1,0,-1,1,1,-1,-1};
// lowest / (1 << 17) >= 1e5 / (1 << 18) >= 2e5 / (1 << 21) >= 1e6
void fastIO() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
}
// file in/out
void setIO(string str = "") {
fastIO();
if (str != "") {
freopen((str + ".in").c_str(), "r", stdin);
freopen((str + ".out").c_str(), "w", stdout);
}
}
// Indexed Set
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
int get_n();
int is_clockwise(int a, int b, int c);
void give_answer(int s);
map<pair<int, pair<int, int>>, int> mp;
int cnt = 800000;
int is_clocki(int a, int b, int c) {
if(mp.find({a, {b, c}}) != mp.end()) {
return mp[{a, {b, c}}];
}
mp[{a, {b, c}}] = is_clockwise(a, b, c);
return mp[{a, {b, c}}];
}
int m, ind = -1;
bool cmp(int a, int b) {
if(is_clocki(ind, a, b)) {
return true;
} else {
return false;
}
}
void solve_() {
m = get_n();
vector<int> ral;
for(int i = 1; i <= m; i++) {
ral.push_back(i);
}
random_shuffle(all(ral));
vector<int> l, r;
int one = ral[0], two = ral[1];
for(int i = 1; i <= m; i++) {
if(i == one || i == two) continue;
if(is_clocki(one, two, i)) {
r.push_back(i);
} else {
l.push_back(i);
}
}
assert(sz(mp) <= m);
ind = ral[0];
sort(all(r), cmp);
r.push_back(one);
sort(all(l), cmp);
l.push_back(two);
assert(sz(mp) <= cnt);
if(sz(r) < sz(l)) {
vector<bool> have_r(m + 1);
for(auto i: r) {
have_r[i] = true;
}
vector<int> mer = r;
for(auto i: l) mer.push_back(i);
vector<int> st;
for(int i = 0; i < sz(mer); i++) {
while(sz(st) >= 2 && !is_clocki(st[sz(st) - 2], st.back(), mer[i])) {
st.pop_back();
}
st.push_back(mer[i]);
}
int sub = 0;
vector<int> bit;
for(auto i: st) {
if(have_r[i]) {
bit.push_back(i);
sub++;
}
}
for(int i = 0; i < sz(bit); i++) {
while(sz(st) >= 2 && !is_clocki(st[sz(st) - 2], st.back(), bit[i])) {
st.pop_back();
}
st.push_back(bit[i]);
}
int nw = sz(st);
cout << nw - sub << '\n';
} else {
vector<bool> have_r(m + 1);
for(auto i: l) {
have_r[i] = true;
}
vector<int> mer = l;
for(auto i: r) mer.push_back(i);
vector<int> st;
for(int i = 0; i < sz(mer); i++) {
while(sz(st) >= 2 && !is_clocki(st[sz(st) - 2], st.back(), mer[i])) {
st.pop_back();
}
st.push_back(mer[i]);
}
int sub = 0;
vector<int> bit;
for(auto i: st) {
if(have_r[i]) {
bit.push_back(i);
sub++;
}
}
for(int i = 0; i < sz(bit); i++) {
while(sz(st) >= 2 && !is_clocki(st[sz(st) - 2], st.back(), bit[i])) {
st.pop_back();
}
st.push_back(bit[i]);
}
int nw = sz(st);
cout << nw - sub << '\n';
}
}
int main() {
fastIO();
auto solve = [&](int test_case)-> void {
while(test_case--) {
solve_();
}
};
int test_cases = 1;
// cin >> test_cases;
solve(test_cases);
return 0;
}
