#include <bits/stdc++.h>
using namespace std;
#define FOR(i, j, k) for(int i=(j); i<=(k); i++)
#define FFOR(i, j, k) for(int i=(j); i<(k); i++)
#define DFOR(i, j, k) for(int i=(j); i>=(k); i--)
#define bug(x) cerr<<#x<<" = "<<(x)<<'\n'
#define pb push_back
#define mp make_pair
#define bit(s, i) (((s)>>(i))&1LL)
#define mask(i) ((1LL<<(i)))
#define builtin_popcount __builtin_popcountll
#define __builtin_popcount __builtin_popcountll
using ll=long long; using ld=long double;
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count()); const ld pi=acos(0)*2;
template <typename T> inline void read(T &x){char c; bool nega=0; while((!isdigit(c=getchar()))&&(c!='-')); if(c=='-'){nega=1; c=getchar();} x=c-48; while(isdigit(c=getchar())) x=x*10+c-48; if(nega) x=-x;}
template <typename T> inline void writep(T x){if(x>9) writep(x/10); putchar(x%10+48);}
template <typename T> inline void write(T x){if(x<0){ putchar('-'); x=-x;} writep(x);}
template <typename T> inline void writeln(T x){write(x); putchar('\n');}
#define taskname "Triangles"
#ifndef Aria
#include "trilib.h"
#else
int get_n(){
int n;
printf("get_n: \n");
read(n);
return n;
}
bool is_clockwise(int a, int b, int c){
printf("is_clockwise %d %d %d: \n", a, b, c);
bool res;
read(res);
return res;
}
void give_answer(int s){
printf("ans = %d\n", s);
}
#endif // Aria
int n;
int a[40001];
#define cw is_clockwise
void quicksort(int l, int r){
if(l>=r) return;
int m=rng()%(r-l+1)+l;
vector <int> left, right;
FOR(i, l, r) if(i!=m) if(cw(1, a[m], a[i])) left.pb(a[i]);
else right.pb(a[i]);
left.pb(a[m]);
m=l+left.size()-1;
for(int x: right) left.pb(x);
FOR(i, l, r) a[i]=left[i-l];
left.clear();
right.clear();
quicksort(l, m-1);
quicksort(m+1, r);
}
deque <int> v;
int main(){
#ifdef Aria
if(fopen(taskname".in", "r"))
freopen(taskname".in", "r", stdin);
#endif // Aria
n=get_n();
FOR(i, 1, n) a[i]=i;
quicksort(2, n);
// FOR(i, 1, n) bug(a[i]);
FOR(i, 1, n){
while(v.size()>=2){
if(cw(v[v.size()-2], v[v.size()-1], a[i])) v.pop_back();
else break;
}
v.pb(a[i]);
}
// bug(v.size());
// for(int x: v) bug(x);
while(true){
int sz=v.size();
while(cw(v.back(), v[0], v[1])) v.pop_front();
while(cw(v[v.size()-2], v.back(), v[0])) v.pop_back();
if(v.size()==sz) break;
}
give_answer(v.size());
}
