//Sylwia Sapkowska
#include <bits/stdc++.h>
#include "trilib.h"
#pragma GCC optimize("O3", "unroll-loops")
using namespace std;
void __print(int x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef LOCAL
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif
#define int long long
typedef pair<int, int> T;
int cw(int a, int b, int c){
if (a == b || b == c || a == c) return 0;
return is_clockwise(a, b, c) ? 1 : -1;
}
void solve(){
int n = get_n();
//just use 1 and 2 to divide
vector<vector<int>>parts(2), hull(2);
parts[0].emplace_back(2);
parts[1].emplace_back(2);
for (int i = 3; i<=n; i++) parts[cw(1, 2, i) == 1 ? 1 : 0].emplace_back(i);
for (int rep = 0; rep < 2; rep++){
stable_sort(parts[rep].begin(), parts[rep].end(), [&](auto x, auto y){return cw(1, x, y) == 1;});
for (auto x: parts[rep]){
while ((int)hull[rep].size() >= 2 && cw(hull[rep].end()[-2], hull[rep].end()[-1], x) == -1) hull[rep].pop_back();
hull[rep].emplace_back(x);
}
if (rep) reverse(hull[rep].begin(), hull[rep].end());
hull[rep].insert(hull[rep].begin(), 1);
// for (auto x: hull[rep]) cout << x << " ";
// cout << "\n";
}
// now we have a heart and we want to merge it
for (int rep = 0; rep < 2; rep++){
hull[rep].pop_back();
while (1){
bool any = 0;
if (hull[0].size() >= 2 && cw(hull[0].end()[-2], hull[0].end()[-1], hull[1].end()[-1]) == -1) {
hull[0].pop_back();
any = 1;
}
if (hull[1].size() >= 2 && cw(hull[0].end()[-1], hull[1].end()[-1], hull[1].end()[-2]) == -1) {
hull[1].pop_back();
any = 1;
}
if (!any) break;
}
for (int i = 0; i<2; i++) reverse(hull[i].begin(), hull[i].end());
hull[0].swap(hull[1]);
}
// for (int rep = 0; rep < 2; rep++){
// for (auto x: hull[rep]) cout << x << " ";
// cout << "\n";
// }
int ans = (int)hull[0].size() + (int)hull[1].size();
// cout << ans << "\n";
give_answer(ans);
}
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
while (t--) solve();
return 0;
}
