#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
#define ll long long
#define ar array
// solution idea: find any point on the hull. a point is on the hull if it isn't contained inside any triangle, so we can maintain this triangle
// after this just use graham scan: sort by angle and then sweep
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n=get_n();
int a=1, b=2, c=3;
for (int i=4; i<=n; ++i) {
bool s1=is_clockwise(a, b, i), s2=is_clockwise(b, c, i), s3=is_clockwise(c, a, i), s4=is_clockwise(a, b, c);
for (int rep=0; rep<3; ++rep) {
if (s1==s3&&s1!=s4) {
a=i;
break;
}
swap(s1, s2);
swap(s2, s3);
swap(a, b);
swap(b, c);
}
}
int fix=a;
vector<int> points;
for (int i=1; i<=n; ++i)
if (i!=fix)
points.push_back(i);
sort(points.begin(), points.end(), [&](int i, int j) { return is_clockwise(fix, j, i); });
vector<int> hull={fix};
for (int i : points) {
while(hull.size()>=2&&is_clockwise(hull.end()[-2], hull.back(), i))
hull.pop_back();
hull.push_back(i);
}
give_answer(hull.size());
return 0;
}
