#include <bits/stdc++.h>
#include "trilib.h"
#define pb push_back
#define X first
#define Y second
#define pii pair<int, int>
using namespace std;
bool ask(int a, int b, int c){
a++; b++; c++;
return is_clockwise(a, b, c);
}
bool cmp(int a, int b){
if(a==b)return 0;
return ask(0, a, b);
}
int main(){
ios_base::sync_with_stdio(false);
int n; n = get_n();
//if(n==3)give_answer(3);
vector<int> up, dw, hull;
dw.pb(1);
for(int i = 2; i < n; i++){
if(ask(0, 1, i))up.pb(i);
else dw.pb(i);
}
sort(up.begin(), up.end(), cmp);
sort(dw.begin(), dw.end(), cmp);
dw.insert(dw.begin(), 0);
for(int i = 0; i < dw.size(); i++){
while(hull.size()>1 && ask(hull.end()[-2], hull.end()[-1], dw[i]))hull.pop_back();
hull.pb(dw[i]);
}
for(int i = 0; i < up.size(); i++){
while(hull.size()>1 && ask(hull.end()[-2], hull.end()[-1], up[i]))hull.pop_back();
hull.pb(up[i]);
}
int sz = hull.size();
for(int i = 0; i < dw.size(); i++){
while(hull.size()>1 && ask(hull.end()[-2], hull.end()[-1], dw[i]))hull.pop_back();
hull.pb(dw[i]);
}
for(int i = 0; i < up.size(); i++){
while(hull.size()>1 && ask(hull.end()[-2], hull.end()[-1], up[i]))hull.pop_back();
hull.pb(up[i]);
}
give_answer(hull.size()-sz);
return 0;
}
