#include "trilib.h"
#include <bits/stdc++.h>
#define eb emplace_back
#define sz(V) ((int)(V).size())
#define befv(V) ((V)[sz(V)-2])
#define allv(V) ((V).begin()),((V).end())
#define sorv(V) sort(allv(V))
#define univ(V) (V).erase(unique(allv(V)),(V).end())
using namespace std;
int ccw(int a, int b, int c) {
if(a == b || b == c || c == a) return 0;
return is_clockwise(a, b, c) ? 1 : -1;
}
vector<int> LV, RV;
int N;
void f(vector<int> &V) {
sort(V.begin()+1, V.end(), [&](int a, int b) {
return 0 < ccw(V[0], a, b);
});
vector<int> T;
for(int v : V) {
for(; 1 < sz(T) && ccw(befv(T), T.back(), v) <= 0; T.pop_back());
T.eb(v);
}
swap(V, T);
}
int main() {
N = get_n();
LV.eb(1); RV.eb(2);
for(int i = 3; i <= N; i++)
(0 < ccw(1, 2, i) ? LV : RV).eb(i);
f(LV); f(RV);
int al = 0, ar = 0, bl = 0, br = 0, ln = sz(LV), rn = sz(RV);
for(bool flag;;) {
flag = false;
for(; 0 < ccw(LV[al], RV[ar], LV[(al+1)%ln]); al=(al+1)%ln) flag = true;
for(; 0 < ccw(LV[al], RV[ar], RV[(ar-1+rn)%rn]); ar=(ar-1+rn)%rn) flag = true;
if(!flag) break;
}
for(bool flag;;) {
flag = false;
for(; ccw(LV[bl], RV[br], LV[(bl-1+ln)%ln]) < 0; bl=(bl-1+ln)%ln) flag = true;
for(; ccw(LV[bl], RV[br], RV[(br+1)%rn]) < 0; br=(br+1)%rn) flag = true;
if(!flag) break;
}
vector<int> Ans;
for(int i = br;; i = (i+1)%rn) {
Ans.eb(RV[i]);
if(i == ar) break;
}
for(int i = al;; i = (i+1)%ln) {
Ans.eb(LV[i]);
if(i == bl) break;
}
sorv(Ans); univ(Ans);
give_answer(sz(Ans));
return 0;
}
