#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;
ll cns = 100000;
unordered_map<ll,bool> cwmap;
bool cwhash(int a, int b, int c){
ll ct = a*cns*cns+b*cns+c;
auto f = cwmap.find(ct);
if (f!=cwmap.end()){
return f->second;
} else {
return cwmap[ct]=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;
}
bool ans;
if (b<c){
ans=cwhash(a,b,c);
} else {
ans=!cwhash(a,c,b);
}
//cout<<ans<<'\n';
return ans;
}
vector<int> convexhull(vector<int> &pts){
/*cout<<"find hull ";
for (int i : pts){
cout<<i<<" ";
}cout<<'\n';*/
if (pts.size()<=3){
return pts;
}
int a = pts[0];
int b = pts[1];
//a to b
vector<int> lhs;
vector<int> rhs;
for (int i = 2; i<pts.size(); 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);
lhs = convexhull(lhs);
rhs = convexhull(rhs);
/*cout<<"merge:\n";
for (int i : lhs){
cout<<i<<" ";
}cout<<'\n';
for (int j : rhs){
cout<<j<<" ";
}cout<<'\n';*/
//now in sorted order
int leftpt = b;
int rs = rhs.size();
int ls = lhs.size();
int rightpt = rhs[0];
int leftind = -1;
int rightind = 0;
for (int i = 0; i<rs; i++){
if (rhs.size()>1&&cw(rhs[(i+1)%rs],rhs[i],leftpt)){
rightpt=rhs[i];
rightind = i;
break;
}
}
assert(rightpt!=-1);
leftind = find(lhs.begin(),lhs.end(),leftpt)-lhs.begin();
//cout<<leftpt<<" "<<rightpt<<'\n';
//cout<<leftind<<" "<<rightind<<'\n';
int lp2 = leftind;
int rp1 = rightind;
bool check;
do {
check = true;
while (lhs.size()>1&&!cw(rhs[rp1],lhs[lp2],lhs[(lp2+1)%ls])){
if (lhs.size()>1&&rhs.size()>1&&!cw(lhs[(lp2+1)%ls],rhs[rp1],rhs[(rp1+rs-1)%rs])&&cw(rhs[rp1],rhs[(rp1+rs-1)%rs],lhs[lp2])){
//check=false;
break;
}
//cout<<"inc lp2\n";
lp2+=1;
lp2%=ls;
check = false;
}
while (rhs.size()>1&&cw(lhs[lp2],rhs[rp1],rhs[(rp1+rs-1)%rs])){
if (lhs.size()>1&&rhs.size()>1&&cw(rhs[(rp1+rs-1)%rs],lhs[lp2],lhs[(lp2+1)%ls])&&!cw(lhs[lp2],lhs[(lp2+1)%ls],rhs[rp1])){
//check=false;
break;
}
//cout<<"dec rp1\n";
rp1+=rs-1;
rp1%=rs;
check = false;
}
} while (!check);
int lp1 = leftind;
int rp2 = rightind;
do {
check = true;
while (lhs.size()>1&&cw(rhs[rp2],lhs[lp1],lhs[(lp1+ls-1)%ls])){
//cout<<"vis\n";
//cout<<lhs[lp1]<<" "<<rhs[rp2]<<'\n';
if (lhs.size()>1&&rhs.size()>1&&cw(lhs[(lp1+ls-1)%ls],rhs[rp2],rhs[(rp2+1)%rs])&&!cw(rhs[rp2],rhs[(rp2+1)%rs],lhs[lp1])){
//check=false;
break;
}
//cout<<"dec lp1\n";
lp1+=ls-1;
lp1%=ls;
check = false;
}
while (rhs.size()>1&&!cw(lhs[lp1],rhs[rp2],rhs[(rp2+1)%rs])){
if (lhs.size()>1&&rhs.size()>1&&!cw(rhs[(rp2+1)%rs],lhs[lp1],lhs[(lp1+ls-1)%ls])&&cw(lhs[lp1],lhs[(lp1+ls-1)%ls],rhs[rp2])){
//check=false;
break;
}
//cout<<"inc rp2\n";
rp2+=1;
rp2%=rs;
check = false;
}
} while (!check);
//cout<<lhs[lp1]<<" "<<lhs[lp2]<<'\n';
//cout<<rhs[rp1]<<" "<<rhs[rp2]<<'\n';
vector<int> hull;
int ptr;
ptr = rp2;
while (ptr!=rp1) {
hull.push_back(rhs[ptr]);
ptr++;
ptr%=rs;
}
hull.push_back(rhs[ptr]);
ptr = lp2;
while (ptr!=lp1) {
hull.push_back(lhs[ptr]);
ptr++;
ptr%=ls;
}
hull.push_back(lhs[ptr]);
/*cout<<"hull contains ";
for (int i : hull){
cout<<i<<' ';
}cout<<'\n';*/
return hull;
}
int main(){
n = get_n();
vector<int> pts(n);
iota(pts.begin(),pts.end(),0);
give_answer(convexhull(pts).size());
}
