#include "trilib.h"
#include <bits/stdc++.h>
using namespace std;
bool cmp(int A, int B) { return is_clockwise(1, A, B); }
vector<int> divi[2]{{2}, {2}}, hull[2];
int main() {
int n = get_n();
for (int i = 3; i <= n; i++) divi[is_clockwise(1, 2, i)].push_back(i);
for (int i = 0; i < 2; i++) {
sort(divi[i].begin(), divi[i].end(), cmp);
for (int j : divi[i]) {
while (hull[i].size() > 1 && is_clockwise(j, hull[i].back(), hull[i][hull[i].size() - 2]))
hull[i].pop_back();
hull[i].push_back(j);
}
if (i) reverse(hull[i].begin(), hull[i].end());
hull[i].insert(hull[i].begin(), 1);
}
if (min(hull[0].size(), hull[1].size()) == 2)
return give_answer(max(hull[0].size(), hull[1].size())), 0;
for (int i = 0; i < 2; i++) {
hull[0].pop_back();
while (true) {
if (hull[0].size() > 1 && is_clockwise(hull[1].back(), hull[0].back(), hull[0][hull[0].size() - 2]))
hull[0].pop_back();
else if (hull[1].size() > 1 && is_clockwise(hull[1][hull[1].size() - 2], hull[1].back(), hull[0].back()))
hull[1].pop_back();
else break;
}
swap(hull[0], hull[1]);
reverse(hull[0].begin(), hull[0].end());
reverse(hull[1].begin(), hull[1].end());
}
give_answer(hull[0].size() + hull[1].size());
return 0;
}
