#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1);
template <class T1, class T2>
inline bool minimise(T1 &x, T2 y)
{
if (x > y)
{
x = y;
return true;
}
return false;
}
template <class T1, class T2>
inline bool maximise(T1 &x, T2 y)
{
if (x < y)
{
x = y;
return true;
}
return false;
}
template <class T>
inline constexpr int sgn(T x)
{
if (x > 0)
return 1;
if (x < 0)
return -1;
return 0;
}
struct Vec2
{
double x, y;
Vec2(double x = 0, double y = 0) : x(x), y(y) {}
inline Vec2 operator+(const Vec2 &oth) const { return Vec2(x + oth.x, y + oth.y); }
inline Vec2 operator-(const Vec2 &oth) const { return Vec2(x - oth.x, y - oth.y); }
inline double norm() const { return sqrt(x * x + y * y); }
inline double norm_sq() const { return x * x + y * y; }
inline Vec2 normalised() const
{
double l = norm();
return Vec2(x / l, y / l);
}
inline static double dot(const Vec2 &v1, const Vec2 &v2)
{
return v1.x * v2.x + v1.y * v2.y;
}
inline static double cross(const Vec2 &v1, const Vec2 &v2)
{
return v1.x * v2.y - v1.y * v2.x;
}
inline static bool is_ccw(const Vec2 &origin, const Vec2 &p1, const Vec2 &p2)
{
Vec2 r1 = p1 - origin;
Vec2 r2 = p2 - origin;
return cross(r1, r2) > 0.;
}
inline static bool is_ray_order(const Vec2 &ray_1, const Vec2 &ray_mid, const Vec2 &ray_2, bool strict = false)
{
int _sgn = sgn(cross(ray_mid, ray_1)) * sgn(cross(ray_mid, ray_2));
if (strict)
return _sgn < 0;
return _sgn <= 0;
}
// inline tuple<const int &, const int &> coords() const
// {
// return tie(x, y);
// }
inline static bool compare_x(const Vec2 &v1, const Vec2 &v2)
{
if (v1.x != v2.x)
return v1.x < v2.x;
return v1.y < v2.y;
}
};
struct Segment
{
Vec2 pt[2];
Segment(Vec2 A, Vec2 B)
{
pt[0] = A, pt[1] = B;
}
inline static bool intersect(Segment p, Segment q, bool strict = false)
{
Vec2 p1 = p.pt[0], p2 = p.pt[1];
Vec2 q1 = q.pt[0], q2 = q.pt[1];
return Vec2::is_ray_order(q1 - p1, p2 - p1, q2 - p1, strict) and
Vec2::is_ray_order(p1 - q1, q2 - q1, p2 - q1, strict);
}
inline static bool intersect_strict(Segment p, Segment q)
{
return intersect(p, q, true);
}
};
// struct Triangulation
// {
// vector<int> adj[MAX];
// };
const int MAX = 1000 + 5;
int N;
Vec2 pt[MAX];
void input()
{
cin >> N;
for (int i = 1; i <= N; i++)
{
int x, y;
cin >> x >> y;
pt[i] = Vec2(x, y);
}
sort(pt + 1, pt + N + 1, Vec2::compare_x);
}
void solve()
{
int ans = 0;
for (int a = 1; a <= N; a++)
for (int b = a + 1; b <= N; b++)
{
bool is_non_crossing = true;
for (int c = 1; c <= N; c++)
for (int d = c + 1; d <= N; d++)
if (Segment::intersect_strict(Segment(pt[a], pt[b]), Segment(pt[c], pt[d])))
is_non_crossing = false;
if (is_non_crossing)
ans++;
}
cout << ans;
}
int main(void)
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
input();
solve();
return 0;
}
