#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
#define vi vector<int>
#define vll vector<ll>
#define vii vector<pair<int, int>>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define loop(_) for (int __ = 0; __ < (_); ++__)
#define pb push_back
#define f first
#define s second
#define sz(_) ((int)_.size())
#define all(_) _.begin(), _.end()
#define lb lower_bound
#define ub upper_bound
using ll = long long;
using ld = long double;
const int N = 1e5 + 7;
const ll mod = 1e9 + 7;
int gn;
int ans;
bool ok(int x, int y)
{
int mask = 0;
for (int i = 1; i <= gn; ++i)
{
if (x == i || y == i || mask == 3)
continue;
mask |= 1 << is_clockwise(x, y, i);
}
return mask != 3;
}
// int solve(vi v)
// {
// if (sz(v) == 0)
// return 0;
// if (sz(v) == 1)
// return 2;
// vi lhs, rhs;
// random_shuffle(all(v));
// int x = v[0], y = v[1];
// for (int i = 2; i < sz(v); ++i)
// {
// int z = v[i];
// (is_clockwise(x, y, z) ? lhs : rhs).pb(z);
// }
// return 2 + solve(lhs) + solve(rhs);
// }
int vis[N];
void dfs(int x)
{
vis[x] = 1;
for (int i = 1; i <= gn; ++i)
{
if (vis[i])
continue;
if (ok(x, i))
{
++ans;
dfs(i);
break;
}
}
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
#ifndef ONLINE_JUDGE
#endif
gn = get_n();
set<int> st;
for (int i = 2; i <= gn; ++i)
{
st.insert(i);
}
while (sz(st) > 1)
{
vi v;
for (auto u : st)
{
v.pb(u);
}
random_shuffle(all(v));
int t = v.back();
vi lhs = {t}, rhs;
for (auto u : v)
{
if (u == t)
continue;
if (!is_clockwise(1, t, u))
{
lhs.pb(u);
}
}
st.clear();
for (auto u : lhs)
st.insert(u);
}
int root = *st.begin();
bool flag = 0;
for (int i = 1; i <= gn; ++i)
{
if (i == root)
continue;
flag |= ok(i, root);
}
assert(flag);
dfs(root);
cout << ++ans;
return 0;
}
