#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
//#define int long long
#include "trilib.h"
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vii;
typedef vector<bool> vb;
typedef long long ll;
typedef pair<ll,ll> pll;
typedef vector<pll> vll;
typedef tree<pii,null_type,less<pii>,rb_tree_tag,
tree_order_statistics_node_update> oset;
#define fi first
#define se second
#define pb push_back
#define pf push_front
#define mid (l+r)/2
#define all(x) x.begin(),x.end()
#define FOR(i,a) for(int i=0;i<(a);i++)
#define FORE(i,a,b) for(int i=(a);i<(b);i++)
#define cont(x) for(auto el:x) cout<<el<<' ';cout<<endl;
#define contp(x) for(auto el:x) cout<<el.fi<<'-'<<el.se<<' ';cout<<endl;
#define sp <<" "<<
#define DEBUG(x) cout<<(#x) sp x<<endl
#define carp(a,b) (((a%MOD)*(b%MOD))%MOD)
#define topla(a,b) (((a%MOD)+(b%MOD))%MOD)
const ll INF=1e18;
const int MAXN=1e5+5;
const int MAXNN=2e5+5;
const int MOD=1e9+7;
vi tut[2];
int piv;
bool mm(int a,int b){
return is_clockwise(piv,a,b);
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int n=get_n();
if(n==3) give_answer(3);
else{
FORE(i,3,n+1){
if(is_clockwise(1,2,i)) tut[0].pb(i);
else tut[1].pb(i);
}
piv=1;
sort(all(tut[0]),mm);
piv=2;
sort(all(tut[1]),mm);
tut[0].pb(1);
tut[1].pb(2);
for(auto el:tut[0]) tut[1].pb(el);
vi vec;
for(auto el:tut[1]){
int sz=vec.size();
while(vec.size()>=2 and !is_clockwise(vec[sz-2],vec[sz-1],el)){
vec.pop_back();
sz=vec.size();
}
vec.pb(el);
}
int cikar=vec.size();
for(auto el:tut[1]){
int sz=vec.size();
while(vec.size()>=2 and !is_clockwise(vec[sz-2],vec[sz-1],el)){
vec.pop_back();
sz=vec.size();
}
vec.pb(el);
}
int ans=vec.size();
ans-=cikar;
give_answer(ans);
}
}
