/*DavitMarg*/
#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string>
#include <cstring>
#include <map>
#include <set>
#include <queue>
#include <iomanip>
#include <stack>
#include <cassert>
#include <iterator>
#include <bitset>
#include <fstream>
#define death
#ifndef death
#include<trilib.h>
#endif // death
#define mod 1000000007ll
#define LL long long
#define LD long double
#define MP make_pair
#define PB push_back
#define all(v) v.begin(),v.end()
using namespace std;
#ifdef death
int get_n()
{
int x;
cin >> x;
return x;
}
vector<pair<LL, LL>> point;
bool is_clockwise(int a, int b, int c)
{
pair<LL, LL> A, B, C;
A = point[a];
B = point[b];
C = point[c];
return A.first * (B.second - C.second) + B.first * (C.second - A.second) + C.first * (A.second - B.second) < 0;
}
void give_answer(int x)
{
cout << x << endl;
}
#endif // death
map<pair<int, pair<int, int>>, bool> used, pre;
bool cw(int a, int b, int c)
{
if (used[MP(a, MP(b, c))])
return pre[MP(a, MP(b, c))];
used[MP(a, MP(b, c))] = 1;
return pre[MP(a, MP(b, c))] = is_clockwise(a, b, c);
}
bool ccw(int a, int b, int c)
{
return !cw(a, b, c);
}
int ans, n;
vector<int> p;
int main()
{
n = get_n();
#ifdef death
point.PB(MP(0,0));
for (int i = 0; i < n; i++)
{
LL x, y;
cin >> x >> y;
point.PB(MP(x,y));
}
#endif // death
srand(6465);
for (int i = 0; i < n; i++)
p.PB(i+1);
random_shuffle(all(p));
for (int i = 0; i < n; i++)
for (int j = i + 1; j < n; j++)
{
int sum = 0;
int cnt = 0;
for (int k = 0; k < n; k++)
{
if (k == i || k == j)
continue;
cnt++;
sum += cw(p[i],p[k], p[j]);
if (sum && sum != cnt)
break;
}
ans += (sum == n - 2 || sum == 0);
}
give_answer(ans);
return 0;
}
