#include "trilib.h"
#include <bits/stdc++.h>
// #pragma GCC optimize("O3")
#define ll long long
#define se second
#define fi first
#define pb push_back
#define lf (id<<1)
#define rg ((id<<1)|1)
#define md ((l+r)>>1)
using namespace std;
typedef pair<ll,ll> pii;
typedef pair<int,pii> ipii;
typedef pair<pii,int> piii;
const int MAXN = 1e7+10;
const int SQRT = 450;
const int INF = 1e9+10;
const int MOD = 998244353;
const int LOG = 30;
int n;
vector<int> up, dw, urut;
bool cmp(int a, int b){
if(is_clockwise(2, a, b)) return 1;
return 0;
}
vector<int> ANS;
void solve(){
ANS.clear();
ANS.pb(urut[0]); ANS.pb(urut[1]);
for(int i=2; i<urut.size(); i++){
while(ANS.size()>=2 && !is_clockwise(
ANS[ANS.size()-2], ANS.back(), urut[i]) ) ANS.pop_back();
ANS.pb(urut[i]);
// cout << urut[i] << " masu masuk\n";
// for(auto in : ANS) cout << in << ' ';
// cout << "\n\n";
}
}
signed main(){
n = get_n();
if(n==3){ give_answer(n); exit(0); }
for(int i=3; i<=n; i++){
if(is_clockwise(1, 2, i)) dw.pb(i);
else up.pb(i);
}
sort(dw.begin(), dw.end(), cmp);
sort(up.begin(), up.end(), cmp);
// for(auto in : up) cout << in << " up\n";
// for(auto in : dw) cout << in << " dw\n";
urut.pb(1);
for(auto in : up) urut.pb(in);
urut.pb(2);
for(auto in : dw) urut.pb(in);
solve();
int ba = ANS.back();
vector<int>vec2;
for(int i=1; i<ANS.size(); i++) vec2.pb(ANS[i]);
vec2.pb(ANS[0]);
urut = vec2;
solve();
give_answer((int)ANS.size());
}
