/*
_____
.' '.
/ 0 0 \
| ^ |
| \ / |
\ '---' /
'._____.'
*/
#include "trilib.h"
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
struct chash
{
int operator()(int x) const
{
x ^= (x >> 20) ^ (x >> 12);
return x ^ (x >> 7) ^ (x >> 4);
}
int operator()(long long x) const
{
return (x ^ (x >> 32) % 1000000007);
}
};
template<typename T> using orderedset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename U> using hashtable = gp_hash_table<T, U, chash>;
template<class T>
void readi(T &x)
{
T input = 0;
bool negative = false;
char c = ' ';
while (c < '-')
{
c = getchar();
}
if (c == '-')
{
negative = true;
c = getchar();
}
while (c >= '0')
{
input = input * 10 + (c - '0');
c = getchar();
}
if (negative)
{
input = -input;
}
x = input;
}
template<class T>
void printi(T output)
{
if (output == 0)
{
putchar('0');
return;
}
if (output < 0)
{
putchar('-');
output = -output;
}
int aout[20];
int ilen = 0;
while(output)
{
aout[ilen] = ((output % 10));
output /= 10;
ilen++;
}
for (int i = ilen - 1; i >= 0; i--)
{
putchar(aout[i] + '0');
}
return;
}
template<class T>
void ckmin(T &a, T b)
{
a = min(a, b);
}
template<class T>
void ckmax(T &a, T b)
{
a = max(a, b);
}
template<class T, class U>
T normalize(T x, U mod = 1000000007)
{
return (((x % mod) + mod) % mod);
}
long long randomizell(long long mod)
{
return ((1ll << 45) * rand() + (1ll << 30) * rand() + (1ll << 15) * rand() + rand()) % mod;
}
int randomize(int mod)
{
return ((1ll << 15) * rand() + rand()) % mod;
}
#define y0 ___y0
#define y1 ___y1
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define debug(x) cerr << #x << " = " << x << endl;
const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-10;
#define MAGIC 347
#define SINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 40013
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
int N;
int ans;
int S;
vector<int> hull;
vector<int> arr;
bool flag[MAXN];
hashtable<int, bool> mp[MAXN];
ll geth(int a, int b)
{
return 1ll * a * N + b;
}
bool ccw(int u, int v, int w)
{
if (mp[u].find(geth(v, w)) != mp[u].end())
{
return mp[u][geth(v, w)];
}
bool res = !(is_clockwise(u + 1, v + 1, w + 1));
mp[u][geth(v, w)] = res; mp[u][geth(w, v)] = !res;
mp[v][geth(w, u)] = res; mp[v][geth(u, w)] = !res;
mp[w][geth(u, v)] = res; mp[w][geth(v, u)] = !res;
return res;
}
bool cmp(int u, int v)
{
return !ccw(u, S, v);
}
void get_hull()
{
sort(arr.begin(), arr.end(), cmp);
hull.PB(S);
for (int v : arr)
{
while(hull.size() >= 2 && !ccw(hull[hull.size() - 2], hull.back(), v))
{
hull.pop_back();
}
hull.PB(v);
}
return;
}
int find(int u, int v)
{
// cerr << "find " << u << ' ' << v << endl;
int net = 0;
for (int i = 0; i < N; i++)
{
if (i == u || i == v) continue;
if (ccw(u, i, v))
{
flag[i] = true;
net++;
}
else
{
flag[i] = false;
net--;
}
}
if (net == N - 2 || net == 2 - N) return u;
arr.clear();
S = (randomize(2) ? u : v);
for (int i = 0; i < N; i++)
{
if (i == u || i == v) continue;
if ((flag[i] && net <= 0) || (!flag[i] && net > 0))
{
arr.PB(i);
}
}
get_hull();
int rand_idx = randomize(hull.size() - 1);
u = hull[rand_idx], v = hull[rand_idx + 1];
hull.clear();
return find(u, v);
}
int solve()
{
if (N == 3)
{
return 3;
}
//find any vertex on the hull
int u = randomize(N), v = (u + 1 + randomize(N - 1)) % N;
S = find(u, v);
arr.clear();
for (int i = 0; i < N; i++)
{
if (S == i) continue;
arr.PB(i);
}
get_hull();
return hull.size();
}
int32_t main()
{
ios_base::sync_with_stdio(0);
srand(time(0));
// cout << fixed << setprecision(10);
// cerr << fixed << setprecision(10);
// if (fopen("input.in", "r"))
// {
// freopen ("input.in", "r", stdin);
// freopen ("output.out", "w", stdout);
// }
N = get_n();
//find any guy on the hull
ans = solve();
give_answer(ans);
// cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
return 0;
}
