#include <bits/stdc++.h>
#include "trilib.h"
#define ll long long
#define ld long double
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define size(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace std;
//mt19937 mt;void random(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll rand(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;
 
void solve()
{
    int n = get_n();
    int ans = 0;
    rep2(i,1,n)
    {
        rep2(j,1,n)
        {
            if(i <= j) continue;
            bool b0 = false;
            bool b1 = false;
            rep2(k,1,n)
            {
                if(k == i || k == j) continue;
                bool w = is_clockwise(i,j,k);
                if(w == true) b1 = true;
                if(w == false) b0 = true;
            }
            if(b1 && b0)
            {
 
            }
            else
            {
                ans++;
            }
        }
    }
    give_answer(ans);
}
 
int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    //random();
    int t = 1;
    //cin >> t;
    while(t--) solve();
}