#include <bits/stdc++.h>
#include "trilib.h"
#define int long long
//#pragma GCC optimize("Ofast")
//#pragma comment(linker, "/stack:200000000")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4")
#define file(s) freopen(s".in","r",stdin); freopen(s".out","w",stdout);
#define forev(i, b, a) for(int i = (b); i >= (a); --i)
#define forn(i, a, b) for(int i = (a); i <= (b); ++i)
#define sz(s) (int)s.size()
#define all(x) x.bg, x.en
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define rbg rbegin()
#define bg begin()
#define en end()
#define s second
#define f first
using namespace std;
typedef pair < long long, long long > pll;
typedef pair < int, int > pii;
typedef unsigned long long ull;
typedef vector < pii > vpii;
typedef vector < int > vi;
typedef long double ldb;
typedef long long ll;
typedef double db;
const int dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1}, block = 265;
const pii base = mp(1171, 3307), Mod = mp(1e9 + 7, 1e9 + 9);
const int inf = 1e9, N = 1e6 + 11, mod = 1e9 + 7;
const db eps = 1e-12, pi = 3.14159265359;
const ll INF = 1e18;
int n, st[N];
vi v1, v2;
bool cmp (int x, int y) { //sort by tga
return is_clockwise(1, x, y);
}
/*
bool is_clockwise (int x, int y, int z) {
cout << "? " << x << ' ' << y << ' ' << z << endl;
int res;
cin >> res;
return res;
}
int get_n () {
cout << "n ?\n";
int n;
cin >> n;
return n;
}
void give_answer (int x) {
cout << "! " << x << endl;
}*/
main () {
ios_base :: sync_with_stdio(0);
// cin.tie(0);
// cout.tie(0);
n = get_n();
forn (i, 3, n)
if (is_clockwise(1, 2, i))
v1.pb(i);
else
v2.pb(i);
sort(all(v1), cmp);
sort(all(v2), cmp);
reverse(all(v1));
v1.pb(2);
reverse(all(v2));
for (auto x : v2)
v1.pb(x);
int Sz = 0;
st[++Sz] = 1;
for (auto x : v1) {
while (Sz > 1 && is_clockwise(st[Sz - 1], st[Sz], x))
--Sz;
st[++Sz] = x;
}
/*
forn (i, 1, Sz)
cout << st[i] << ' ';
cout << endl;*/
int pr = 1, suff = Sz;
bool ok = 1;
while (ok && suff - pr + 1 >= 3) { //triangle is always convex
ok = 0;
if (is_clockwise(st[suff], st[pr], st[pr + 1]))
++pr, ok = 1;
else if (!is_clockwise(st[pr], st[suff], st[suff - 1]))
--suff, ok = 1;
}
give_answer(suff - pr + 1);
return 0;
}
