#include<bits/stdc++.h>
#include"trilib.h"
typedef long long ll;
typedef long double ld;
#define vii vector<pair<int, int>>
#define vi vector<int>
#define vl vector<long long>
#define vll vector<pair<long long, long long>>
#define mp make_pair
#define pb push_back
#define rep(i, a, b) for(int i = a;i<=b;i++)
#define f first
#define s second
#define FIO ios_base::sync_with_stdio(0);cin.tie(0);
#define start int tt;cin>>tt;rep(testcase, 1, tt)
#define print(k) cout<<"Case #"<<testcase<<": "<<k<<"\n";
#define endl "\n"
#define DEBUG(k) cerr<<k<<"\n";
int main () {
int n = get_n(), ans = 0;
rep(i, 1, n) {
rep(j, i+1, n) {
bool check = true, check2 = true;
rep(k, 1, n) {
if(k == i or k == j)continue;
bool d= !is_clockwise(i, j, k);
check&=d;
check2&=!d;
if(!check and !check2)break;
}
ans+=check;
ans+=check2;
}
}
give_answer(ans);
}
