#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
typedef pair<int, int> pii;
const int MX=40010;
int n;
map<pii, bool> mem[MX];
bool ccw(int a, int b, int c){
if(mem[a].find({b,c})!=mem[a].end()) return mem[a][pii(b,c)];
if(mem[a].find({c,b})!=mem[a].end()) return !mem[a][pii(c,b)];
return mem[a][pii(b,c)]=is_clockwise(a,b,c);
}
vector<int> L, R;
vector<int> get_hull(int s, vector<int> V){
sort(V.begin(), V.end(), [=](int a, int b){ return ccw(s,a,b); });
vector<int> R;
R.push_back(s);
for(int v:V){
while(R.size()>=2U && !ccw(R[R.size()-2], R[R.size()-1], v)) R.pop_back();
R.push_back(v);
}
return R;
}
vector<int> all_hull(int v){
vector<int> V;
for(int i=1; i<=n; i++) if(i!=v) V.push_back(i);
return get_hull(v, V);
}
int solve(){
for(int i=3; i<=n; i++){
if(ccw(1,2,i)) R.push_back(i);
else L.push_back(i);
}
if(L.empty() || R.empty()) return all_hull(1).size();
if(L.size()==1U) return all_hull(L[0]).size();
if(R.size()==1U) return all_hull(R[0]).size();
vector<int> LH, RH;
LH=get_hull(1, L), RH=get_hull(2, R);
int u=-1, v=-1, p=-1, q=-1;
// upper tangent
for(int p1=0, p2=0, lsz=LH.size(), rsz=RH.size(); p1<lsz; p1++){
while(true){
int a=(p2+rsz-1)%rsz, b=(p2+1)%rsz;
if(!ccw(LH[p1], RH[p2], RH[a])){ p2=a; continue; }
if(!ccw(LH[p1], RH[p2], RH[b])){ p2=b; continue; }
break;
}
int a=(p1+lsz-1)%lsz, b=(p1+1)%lsz;
if(ccw(RH[p2], LH[p1], LH[a])) continue;
if(ccw(RH[p2], LH[p1], LH[b])) continue;
assert(u<0 && v<0);
u=p1, v=p2;
break;
}
// lower tangent
for(int p1=0, p2=0, lsz=LH.size(), rsz=RH.size(); p1<lsz; p1++){
while(true){
int a=(p2+rsz-1)%rsz, b=(p2+1)%rsz;
if(ccw(LH[p1], RH[p2], RH[a])){ p2=a; continue; }
if(ccw(LH[p1], RH[p2], RH[b])){ p2=b; continue; }
break;
}
int a=(p1+lsz-1)%lsz, b=(p1+1)%lsz;
if(!ccw(RH[p2], LH[p1], LH[a])) continue;
if(!ccw(RH[p2], LH[p1], LH[b])) continue;
assert(p<0 && q<0);
p=p1, q=p2;
break;
}
int cnt=0, pos;
pos=v;
while(true){
cnt++;
if(pos==q) break;
pos=(pos+1)%RH.size();
}
pos=p;
while(true){
cnt++;
if(pos==u) break;
pos=(pos+1)%LH.size();
}
return cnt;
}
int main(){
n=get_n();
give_answer(solve());
return 0;
}
