// author: erray
#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
#ifdef DEBUG
#include "/home/eagle/debug.h"
#else
#define debug(...) void(37)
#endif
mt19937 rng(37);
int main() {
int N = get_n(); //init is here
auto Ask = [&](int a, int b, int c) {
return is_clockwise(a + 1, b + 1, c + 1);
};
int pivot = uniform_int_distribution<int>(0, N - 1)(rng);
function<vector<int>(vector<int>)> Dfs = [&](vector<int> p) {
int s = int(p.size());
if (s < 2) {
return p;
}
int mid = uniform_int_distribution<int>(0, s - 1)(rng);
array<vector<int>, 2> split;
for (int i = 0; i < s; ++i) {
if (i != mid) {
split[Ask(pivot, p[mid], p[i])].push_back(p[i]);
}
}
auto left = Dfs(split[0]);
left.push_back(p[mid]);
auto right = Dfs(split[1]);
left.insert(left.end(), right.begin(), right.end());
return left;
};
vector<int> ord(N);
iota(ord.begin(), ord.end(), 0);
ord.erase(ord.begin() + pivot);
ord = Dfs(ord);
bool pivot_convex = true;
for (int i = 0; i < N; ++i) {
if (i != ord.back() && i != pivot) {
pivot_convex &= Ask(ord.back(), pivot, i);
}
}
if (pivot_convex) {
ord.push_back(pivot);
}
vector<int> st;
for (auto i : ord) {
while (int(st.size()) >= 2 && !Ask(st[int(st.size()) - 2], st.back(), i)) {
st.pop_back();
}
}
cout << int(st.size()) << '\n';
}
