#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
#define FOR(i,a) for (int i=0;i<(a);++i)
#define FORD(i,a) for (int i=(a)-1;i>=0;i--)
#define FORT(i,a,b) for (int i=(a);i<=(b);++i)
#define FORTD(i,b,a) for (int i=(b);i>=(a);--i)
#define trav(i,v) for (auto i : v)
#define all(v) v.begin(),v.end()
#define ad push_back
#define fr first
#define sc second
#define mpr(a,b) make_pair(a,b)
#define pir pair<int,int>
#define all(v) v.begin(),v.end()
#define make_unique(v) v.erase(unique(all(v),v.end()))
#define fastio ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define dbg(x);
#define dbgv(v);
#define srng mt19937 rng(chrono::steady_clock::now().time_since_epoch().count())
#define y1 EsiHancagorcRepa
#ifdef ALEXPC
#define dbg(x); cout<<#x<<" = "<<x<<endl
#define dbgv(v); cout<<#v<<" = ["; trav(tv,v)cout<<"tv,";cout<<"]"<<endl
#endif
//const int N=100,M=N*N;
const ll MOD=1000*1000*1000+7;
const int N=1e5+6;
int main(){
fastio;
srng;
int n=get_n(),ans=0;
srand(68465);
vector<int> v;
FOR(i,n)v.ad(i+1);
random_shuffle(all(v));
FOR(i1,n){
FORT(i2,i1+1,n-1){
//if (i1==i2)continue;
int tv=0;
int qan=0;
FOR(i,n){
if (i==i1 || i==i2)continue;
tv+=is_clockwise(v[i1],v[i],v[i2] );
qan++;
if (tv!=0 && tv!=qan){
break;
}
}
if (tv==n-2 || tv==0){
ans++;
}
}
}
give_answer(ans);
return 0;
}
