#include <iostream>
#include <vector>
#include <set>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <stdio.h>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <fstream>
#include <complex>
#include <random>
#include <stack>
#include <unordered_map>
#include <chrono>
#include <set>
#define FOR(i,n) for(int i=0;i<n;i++)
#define FORE(i,a,b) for(int i=a;i<=b;i++)
#define ll long long int
#define vi vector<int>
#define ii pair<int,int>
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define pll pair<ll,ll>
#define cd complex<double>
#define ld long double
#define pld pair<ld,ld>
#define iii pair<ii,int>
#define vv vector
#include "trilib.h"
using namespace std;
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
/*
ii pnts[6] = {{1,1},{4,3},{2,2},{1,4},{5,1},{3,2}} ;
int get_n(){
//pnts = {}
return 6;
}
int cross(ii a,ii b,ii c){
int x1 = a.ff-c.ff;
int x2 = b.ff-c.ff;
int y1 = a.ss-c.ss;
int y2 = b.ss-c.ss;
return x1*y2-x2*y1;
}
bool is_clockwise(int a,int b,int c){
a--;b--;c--;
return cross(pnts[a],pnts[b],pnts[c]) < 0;
}
*/
int ctr = 0;
bool is_c(int a,int b,int c){
ctr++;
if(ctr == 1e6)return 6/0;
return is_clockwise(a,b,c);
}
int getRand(int n){
return rng() % n;
}
int n;
int* arr;
int countCl(int a,int b){
random_shuffle(arr,arr+n,getRand);
FOR(i,n){
if(arr[i] == a or arr[i] == b)continue;
if(is_clockwise(a,b,arr[i]))return arr[i];
}
return -1;
}
int findCorner(){
random_shuffle(arr,arr+n,getRand);
int a = arr[0];
int b = arr[1];
int cnt = 0;
while(1){
cnt++;
int nd = countCl(a,b);
if(nd == -1)break;
if(cnt%2 == 0){
a = nd;
}else{
b = nd;
}
}
return a;
}
int hull(int c){
//return 0;
int p[n];
FOR(i,n){
p[i] = i+1;
}
swap(p[0],p[c-1]);
//return 0;
sort(p+1,p+n,[&](int a,int b){
return !is_clockwise(c,a,b);
});
deque<int> st;
int ptr = 0;
//return 0;
//cout << "got here" << endl;
while(1){
while(st.size() > 1 and is_clockwise(st[(int)st.size()-2],st[(int)st.size()-1],p[ptr]))st.pop_back();
st.push_back(p[ptr]);
ptr++;
if(ptr == n)break;
}
while(st.size() > 1 and is_clockwise(st[(int)st.size()-2],st[(int)st.size()-1],p[0]))st.pop_back();
return st.size();
}
int main(){
n = get_n();
arr = new int[n];
FOR(i,n)arr[i] = i+1;
give_answer(hull(findCorner()));
return 0;
}
