#include<bits/stdc++.h>
#include<trilib.h>
using namespace std;
int getn(){
int n;
//scanf("%d", &n);
n = get_n();
return n;
}
bool isclokwise(int x, int y, int z){
int ok;
//printf("%d %d %d\n",x, y, z ), scanf("%d", &ok);;
ok = is_clockwise(x, y, z);
return ok;
}
void giveans(int x){
//printf("%d\n",x );
give_answer(x);
}
bool comp(int x, int y){
return isclokwise(1, x, y);
}
vector<int> qualmetade[5], hull[5];
int n;
int main(){
n = getn();
qualmetade[0].push_back(2);
qualmetade[1].push_back(2);
for(int i = 3; i <= n; i++){
if(isclokwise(1, 2, i)) qualmetade[1].push_back(i);
else qualmetade[0].push_back(i);
}
for(int metade = 0; metade <= 1; metade++){
sort(qualmetade[metade].begin(), qualmetade[metade].end(), comp);
for(int i = 0; i < qualmetade[metade].size(); i++){
int esse= qualmetade[metade][i];
int tam = hull[metade].size();
while(tam >= 2 && !isclokwise(hull[metade][tam - 2], hull[metade][tam - 1], esse)){
tam--;
hull[metade].pop_back();
}
hull[metade].push_back(esse);
}
if(metade)reverse(hull[1].begin(), hull[1].end());
hull[metade].insert(hull[metade].begin(), 1);
//hull[1].insert(hull[1].begin(), 1);
}
//printf("%d %d\n", hull[0].size(), hull[1].size() );
if(min(hull[0].size(), hull[1].size()) == 2){
giveans(max(hull[0].size(), hull[1].size()));
//printf("oi\n");
return 0;
}
for(int metade = 0; metade <= 1; metade++){
hull[0].pop_back();
while(true){
bool quebra = true;
int tam = hull[0].size();
if(tam >= 2 && !isclokwise(hull[0][tam-2], hull[0][tam - 1],
hull[1][hull[1].size() - 1])){
hull[0].pop_back();
quebra = false;
}
tam = hull[1].size();
if(tam >= 2 && !isclokwise(hull[0][hull[0].size() - 1], hull[1][tam-1], hull[1][tam - 2])){
hull[1].pop_back();
quebra = false;
}
if(quebra) break;
}
for(int i = 0; i <= 1; i++) reverse(hull[i].begin(), hull[i].end());
swap(hull[0], hull[1]);
}
giveans(hull[0].size() + hull[1].size());
}
