// Mateusz Radecki
// Queries: O(n*log(n))
// Complexity: O(n*log(n))
//Testing
#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
int n;
vector <int> divide[2], hull[2];
bool is_less(int a, int b)
{
return is_clockwise(1, a, b);
}
int main()
{
n=get_n();
divide[0]=divide[1]={2};
for (int i=3; i<=n; i++)
divide[is_clockwise(1, 2, i)].push_back(i);
for (int h=0; h<2; h++)
{
sort(divide[h].begin(), divide[h].end(), is_less);
for (int i : divide[h])
{
int r=hull[h].size();
while (r>1 && !is_clockwise(hull[h][r-2], hull[h][r-1], i))
{
r--;
hull[h].pop_back();
}
hull[h].push_back(i);
}
if (h)
reverse(hull[h].begin(), hull[h].end());
hull[h].insert(hull[h].begin(), 1);
}
if ((int)min(hull[0].size(), hull[1].size())==2)
{
give_answer(max(hull[0].size(), hull[1].size()));
return 0;
}
give_answer(hull[0].size()+hull[1].size()-2);
return 0;
}
