#include<bits/stdc++.h>
#include "trilib.h"
using namespace std;
#define inf 5e18
#define nl '\n'
int P;
bool cmp(int a, int b){
return is_clockwise(P, a, b);
}
deque<int> func(deque<int>& v, int p){
P = p;
sort(v.begin(), v.end(), cmp);
deque<int> ans;
ans.push_back(p);
for(int x : v){
while(ans.size() >= 2 and !is_clockwise(ans[ans.size()-2], ans.back(), x)) ans.pop_back();
ans.push_back(x);
}
return ans;
}
inline void solve(){
int n = get_n();
deque<int> a, b;
for(int i=3; i<=n; i++){
(is_clockwise(1, 2, i) ? b : a).push_back(i);
}
a = func(a, 1);
b = func(b, 2);
for(int i=0; i<10; i++){
while(a.size() >= 2 and b.size() >= 1 and !is_clockwise(b.back(), a[0], a[1])) a.pop_front();
while(a.size() >= 1 and b.size() >= 2 and !is_clockwise(b[b.size()-2], b.back(), a[0])) b.pop_back();
while(a.size() >= 1 and b.size() >= 2 and !is_clockwise(a.back(), b[0], b[1])) b.pop_front();
while(a.size() >= 2 and b.size() >= 1 and !is_clockwise(a[a.size()-2], a.back(), b[0])) a.pop_back();
}
give_answer(a.size()+b.size());
}
signed main(){
int t = 1;
//cin>>t;
while(t--) solve();
return 0;
}
