#include "trilib.h"
//#include "trilib.c"
#include <bits/extc++.h>
using namespace std;
using namespace __gnu_pbds;
#define fast ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define all(a) a.begin(), a.end()
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using vi = vector<int>;
using oset = tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>;
random_device rd;
mt19937 rnd(rd());
bool is_inside(int a, int b, int c, int d) {
bool x = is_clockwise(a, b, d), y = is_clockwise(b, c, d), z = is_clockwise(c, a, d);
return (x == y && y == z);
}
int O;
bool comp(int x, int y) {
return is_clockwise(O, y, x);
}
int main() {
int n = get_n();
vi r(n);
iota(all(r), 1);
shuffle(all(r), rnd);
int a = r[0], b = r[1], c = r[2];
for (int i = 3; i < n; ++i) {
if (!is_clockwise(a, b, c))
swap(b, c);
if (is_clockwise(a, b, r[i])) {
if (is_inside(a, b, r[i], c))
c = r[i];
}
else if (is_clockwise(b, c, r[i])) {
if (is_inside(b, c, r[i], a))
a = r[i];
}
else if (is_inside(a, c, r[i], b))
b = r[i];
}
O = a;
vi p(n - 1);
for (int i = 1; i < O; ++i)
p[i - 1] = i;
for (int i = O + 1; i <= n; ++i)
p[i - 2] = i;
sort(all(p), comp);
vi st;
st.push_back(O);
for (int i: p) {
while (st.size() > 1 && is_clockwise(st[(int)st.size() - 2], st.back(), i))
st.pop_back();
st.push_back(i);
}
give_answer((int)st.size());
}
