#include "trilib.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 501;
int n;
vector<int> divide[2];
vector<int> hull[2];
bool comp(int a, int b) {
if (a == b) return false;
return is_clockwise(1, a, b);
}
bool call_is_clockwise(int a, int b, int c) {
bool res = is_clockwise(a, b, c);
//cout << a << " " << b << " " << c << " " << res << endl;
return res;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
n = get_n();
for (int i = 0; i < 2; i++) divide[i].push_back(2);
for (int i = 3; i <= n; i++) {
divide[is_clockwise(1, 2, i)].push_back(i);
}
for (int tp = 0; tp < 2; tp++) {
sort(divide[tp].begin(), divide[tp].end(), comp);
for (int i : divide[tp]) {
int r = hull[tp].size();
while (r > 1 && !call_is_clockwise(hull[tp][r - 2], hull[tp][r - 1], i)) {
r--;
hull[tp].pop_back();
}
hull[tp].push_back(i);
}
if (tp) reverse(hull[tp].begin(), hull[tp].end());
hull[tp].insert(hull[tp].begin(), 1);
}
if (min(hull[0].size(), hull[1].size()) == 1)
{
give_answer(max(hull[0].size(), hull[1].size()));
return 0;
}
/*
for (int i : hull[0]) cout << i << " ";
cout << endl;
for (int i : hull[1]) cout << i << " ";
cout << endl; */
for (int i = 0; i < 2; i++) {
hull[0].pop_back();
while (true) {
bool good = true;
if (!call_is_clockwise(hull[0][hull[0].size() - 2], hull[0][hull[0].size() - 1], hull[1].back())) {
good = false;
hull[0].pop_back();
}
if (!call_is_clockwise(hull[0].back(), hull[1][hull[1].size() - 1], hull[1][hull[1].size() - 2])) {
good = false;
hull[1].pop_back();
}
if (good) break;
}
for (int tp = 0; tp < 2; tp ++) reverse(hull[tp].begin(), hull[tp].end());
swap(hull[0], hull[1]);
}
give_answer(hull[0].size() + hull[1].size());
}
/*
6
1 1
4 3
2 2
1 4
5 1
3 2
*/
