#include "trilib.h"
#include <bits/stdc++.h>
#define ll long long
using namespace std;
vector<int> hull = {1, 2, 3};
bool side;
signed main()
{
int N = get_n();
side = is_clockwise(1, 2, 3);
for (int i = 4; i <= N; i++)
{
//for (int j = 0; j < hull.size(); j++)
//cerr << hull[j] << " \n"[j == hull.size() - 1];
if (is_clockwise(hull.back(), i, hull.front()) == side)
{
//cerr << "insert" << i << '\n';
hull.emplace_back(i);
while (hull.size() >= 3 && is_clockwise(hull[hull.size() - 3], hull[hull.size() - 2], hull[hull.size() - 1]) != side)
hull.erase(hull.begin() + (hull.size() - 2));
while (hull.size() >= 3 && is_clockwise(hull[hull.size() - 1], hull[0], hull[1]) != side)
hull.erase(hull.begin());
}
else
{
int L = 0, R = hull.size() - 1;
while (R - L > 1)
{
int mid = (L + R) / 2;
if (is_clockwise(hull[L], i, hull[mid]) == side)
R = mid;
else
L = mid;
}
//cerr << i << "final range:" << L << ", " << R << '\n';
if (is_clockwise(hull[L], i, hull[R]) == side)
{
//cerr << "insert" << i << '\n';
hull.insert(hull.begin() + R, i);
int pos = R;
while (hull.size() >= 3 && is_clockwise(hull[pos], hull[(pos + 1) % hull.size()], hull[(pos + 2) % hull.size()]) != side)
{
int poppos = (pos + 1) % hull.size();
hull.erase(hull.begin() + ((pos + 1) % hull.size()));
if (poppos < pos)
pos--;
}
while (hull.size() >= 3 && is_clockwise(hull[pos], hull[(pos + hull.size() - 1) % hull.size()], hull[(pos + hull.size() - 2) % hull.size()]) == side)
{
int poppos = (pos + hull.size() - 1) % hull.size();
hull.erase(hull.begin() + ((pos - 1) % hull.size()));
if (poppos < pos)
pos--;
}
}
}
}
give_answer(hull.size());
}
/*
6
1 1
4 3
2 2
1 4
5 1
3 2
*/
