#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;
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 main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
#ifndef ONLINE_JUDGE
#endif
gn = get_n();
int ans = 0;
for (int i = 1; i <= gn; ++i)
{
for (int j = 1; j < i; ++j)
{
ans += ok(i, j);
}
}
cout << ans;
return 0;
}
