#include "trilib.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
/*
int get_n();
int is_clockwise(int a, int b, int c);
void give_answer(int s);
*/
int n;
int cns = 40000;
unordered_map<int,bool> cwmap[40000];
int numhashed = 0;
bool cwhash(int a, int b, int c){
int ct = b*cns+c;
auto f = cwmap[a].find(ct);
if (f!=cwmap[a].end()){
return cwmap[a][ct];
} else {
if (numhashed<=1000000){
numhashed++;
return cwmap[a][ct]=bool(is_clockwise(a+1,b+1,c+1));
} else {
return bool(is_clockwise(a+1,b+1,c+1));
}
}
}
bool cw(int a, int b, int c){
//cout<<"cw "<<a<<" "<<b<<" "<<c<<" ";
int minv = min(min(a,b),c);
int tmp;
if (a!=minv){
tmp=a;a=b;b=c;c=tmp;
}
if (a!=minv){
tmp=a;a=b;b=c;c=tmp;
}
if (b<c){
return cwhash(a,b,c);
} else {
return !cwhash(a,c,b);
}
//cout<<ans<<'\n';
}
/*int pcnt = 0;
bool cw(int a, int b, int c){
pcnt++;
assert(pcnt<=1000000);
return is_clockwise(a+1,b+1,c+1);
}*/
vector<int> pts;
vector<int> rhs;
vector<int> lhs;
vector<int> hull;
int convexhull(int s, int e){
/*cout<<s<<" "<<e<<'\n';
cout<<"find hull ";
for (int i = s; i<e; i++){
cout<<pts[i]<<" ";
}cout<<'\n';*/
if (e-s<=3){
if (e-s==3&&!cw(pts[s],pts[s+1],pts[s+2])){
swap(pts[s+1],pts[s+2]);
}
return e-s;
}
int a = pts[s];
int b = pts[s+1];
//a to b
lhs.clear();
rhs.clear();
for (int i = s+2; i<e; i++){
if (cw(a,b,pts[i])){
lhs.push_back(pts[i]);
} else {
rhs.push_back(pts[i]);
}
}
if (lhs.size()>rhs.size()){
swap(lhs,rhs);
swap(a,b);
}
lhs.push_back(a);
lhs.push_back(b);
assert(s+lhs.size()+rhs.size()==e);
for (int i = s; i<s+lhs.size(); i++){
pts[i]=lhs[i-s];
}
for (int i = s+lhs.size(); i<e; i++){
pts[i]=rhs[i-s-lhs.size()];
}
/*cout<<"lhs: ";
for (int i : lhs){
cout<<i<<" ";
}cout<<'\n';
cout<<"rhs: ";
for (int i : rhs){
cout<<i<<" ";
}cout<<'\n';
for (int i : pts){
cout<<i<<" ";
}cout<<'\n';*/
int rf = rhs.size();
int lf = lhs.size();
int ls = convexhull(s,s+lf);
int rs = convexhull(s+lf,e);
/*cout<<"merge:\n";
for (int i = s; i<s+ls; i++){
cout<<pts[i]<<" ";
}cout<<'\n';
for (int j = s+lf;j<s+lf+rs; j++){
cout<<pts[j]<<" ";
}cout<<'\n';*/
//now in sorted order
int leftpt = b;
int rightpt = pts[s+lf];
int leftind = -1;
int rightind = 0;
for (int i = 0; i<rs; i++){
if (rf>1&&cw(pts[s+lf+(i+1)%rs],pts[s+lf+i],leftpt)){
rightpt=pts[s+lf+i];
rightind = i;
break;
}
}
assert(rightpt!=-1);
leftind = find(pts.begin()+s,pts.begin()+s+lf,leftpt)-(pts.begin()+s);
//cout<<leftpt<<" "<<rightpt<<'\n';
//cout<<leftind<<" "<<rightind<<'\n';
int lp2 = leftind;
int rp1 = rightind;
bool check;
bool condexit;
do {
check = true;
condexit = true;
while (ls>1&&!cw(pts[s+lf+rp1],pts[s+lp2],pts[s+(lp2+1)%ls])){
if (ls>1&&rs>1&&!cw(pts[s+(lp2+1)%ls],pts[s+lf+rp1],pts[s+lf+(rp1+rs-1)%rs])&&cw(pts[s+lf+rp1],pts[s+lf+(rp1+rs-1)%rs],pts[s+lp2])){
//check=false;
condexit = false;
break;
}
//cout<<"inc lp2\n";
lp2+=1;
lp2%=ls;
check = false;
}
while (rs>1&&cw(pts[s+lp2],pts[s+lf+rp1],pts[s+lf+(rp1+rs-1)%rs])){
if (ls>1&&rs>1&&cw(pts[s+lf+(rp1+rs-1)%rs],pts[s+lp2],pts[s+(lp2+1)%ls])&&!cw(pts[s+lp2],pts[s+(lp2+1)%ls],pts[s+lf+rp1])){
//check=false;
condexit = false;
break;
}
//cout<<"dec rp1\n";
rp1+=rs-1;
rp1%=rs;
check = false;
}
} while (!check);
assert(condexit==true);
int lp1 = leftind;
int rp2 = rightind;
do {
check = true;
condexit = true;
while (ls>1&&cw(pts[s+lf+rp2],pts[s+lp1],pts[s+(lp1+ls-1)%ls])){
//cout<<"vis\n";
//cout<<pts[s+lp1]<<" "<<pts[s+ls+rp2]<<'\n';
if (ls>1&&rs>1&&cw(pts[s+(lp1+ls-1)%ls],pts[s+lf+rp2],pts[s+lf+(rp2+1)%rs])&&!cw(pts[s+lf+rp2],pts[s+lf+(rp2+1)%rs],pts[s+lp1])){
//check=false;
condexit = false;
break;
}
//cout<<"dec lp1\n";
lp1+=ls-1;
lp1%=ls;
check = false;
}
while (rs>1&&!cw(pts[s+lp1],pts[s+lf+rp2],pts[s+lf+(rp2+1)%rs])){
if (ls>1&&rs>1&&!cw(pts[s+lf+(rp2+1)%rs],pts[s+lp1],pts[s+(lp1+ls-1)%ls])&&cw(pts[s+lp1],pts[s+(lp1+ls-1)%ls],pts[s+lf+rp2])){
//check=false;
condexit = false;
break;
}
//cout<<"inc rp2\n";
rp2+=1;
rp2%=rs;
check = false;
}
} while (!check);
assert(condexit==true);
//cout<<pts[s+lp1]<<" "<<pts[s+lp2]<<'\n';
//cout<<pts[s+ls+rp1]<<" "<<pts[s+ls+rp2]<<'\n';
hull.clear();
int ptr;
ptr = rp2;
while (ptr!=rp1) {
hull.push_back(pts[s+lf+ptr]);
ptr++;
ptr%=rs;
}
hull.push_back(pts[s+lf+ptr]);
ptr = lp2;
while (ptr!=lp1) {
hull.push_back(pts[s+ptr]);
ptr++;
ptr%=ls;
}
hull.push_back(pts[s+ptr]);
for (int i = s; i<s+hull.size(); i++){
pts[i]=hull[i-s];
}
/*cout<<"hull contains ";
for (int i : hull){
cout<<i<<' ';
}cout<<'\n';*/
int hs = hull.size();
return hs;
}
int main(){
n = get_n();
pts.resize(n);
iota(pts.begin(),pts.end(),0);
std::mt19937 g(1234588);
shuffle(pts.begin(),pts.end(),g);
give_answer(convexhull(0,n));
}
