#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define il inline
const int N = 4e3 + 5;

const double eps = 1e-8;
il int sgn(double x)
{
    // 进行判断, 提高精度
    if (fabs(x) <= eps)
        return 0;          // x == 0, 精度范围内的近似相等
    return x > 0 ? 1 : -1; // 返回正负
}
il bool eq(double a, double b) { return abs(a - b) < eps; } // ==
il bool le(double a, double b) { return a - b < eps; }      // <=
il bool lt(double a, double b) { return a - b < -eps; }     // <
typedef struct Point
{
    int x, y;
    int id;
    // Point(double x = 0, double y = 0) : x(x), y(y) {} // 构造函数, 初始值为 0

    // 重载运算符
    // 点 - 点 = 向量 (向量AB = B - A)
    Point operator-(const Point &B) const { return Point(x - B.x, y - B.y); }

    // 点 + 点 = 点, 点 + 向量 = 向量, 向量 + 向量 = 向量
    Point operator+(const Point &B) const { return Point(x + B.x, y + B.y); }

    // 向量 · 向量 (点积)
    double operator*(const Point &B) const { return x * B.x + y * B.y; }

    // 向量 × 向量 (叉积)
    double operator^(const Point &B) const { return x * B.y - y * B.x; }

    // 判断大小, 一般用于排序
    bool operator<(const Point &B) const { return x < B.x || (x == B.x && y < B.y); }

} Vector;

using Points = vector<Point>;

// 极角排序
// Need: (^, sgn)
// 基准点
Point p0;
il double theta(auto p) { return atan2(p.y, p.x); } // 求极角
void psort(Points &ps, Point c = p0)              // 极角排序
{
    sort(ps.begin(), ps.end(), [&](auto p1, auto p2) {
        return lt(theta(p1 - c), theta(p2 - c));
    });
}

// 凸包
// Andrew算法求凸包，最后一个点与第一个点重合
// Need: (^,-,<), sgn, le
il bool check(Point p, Point q, Point r) { return le(0, (q - p) ^ (r - q)); }
vector<Point> Andrew(Points poly)
{
    int n = poly.size(), top = 0;
    vector<int> stk(n + 10, 0), used(n + 10, 0);
    sort(poly.begin(), poly.end());
    stk[++top] = 0;
    for (int i = 1; i < n; i++)
    {
        while (top > 1 && sgn((poly[stk[top]] - poly[stk[top - 1]]) ^ (poly[i] - poly[stk[top]])) <= 0)
            used[stk[top--]] = 0;

        used[i] = 1;
        stk[++top] = i;
    }
    int tmp = top;
    for (int i = n - 2; i >= 0; i--)
    {
        if (used[i]) continue;
        while (top > tmp && sgn((poly[stk[top]] - poly[stk[top - 1]]) ^ (poly[i] - poly[stk[top]])) <= 0)
            used[stk[top--]] = 0;

        used[i] = 1;
        stk[++top] = i;
    }
    vector<Point> a;
    for (int i = 1; i <= top; i++) a.push_back(poly[stk[i]]);
    return a;
}

Point temp[N];
bool vis[N];
void solve()
{
    int n;
    cin >> n;
    Points ans, p;
    for (int i = 0; i < n; i++)
    {
        int a, b;
        cin >> a >> b;
        p.push_back({a, b, i});
    }
    ans = Andrew(p);

    // unordered_map<int, int> mp;
    for (auto [x, y, id]: ans) vis[id] = 1;

    int res = 0;
    for (int i = 0; i < n; i++)
    {
        // if (n == 2000) 
        // {
        //     if (i == 500) 
        //     {
        //         cout << res << endl;
        //         return;
        //     }
        // }
        auto [x, y, id] = p[i];
        if (vis[id]) continue;

        p0 = p[i];
        int tn = 0;
        for (int j = 0; j < n; j++) 
        {
            if (j != i) temp[tn++] = p[j];
        }
        sort(temp, temp + tn, [&](auto p1, auto p2) {
            return lt(theta(p1 - p0), theta(p2 - p0));
        });

        for (int j = 0; j < tn; j++)
        {
            auto p1 = temp[j], p2 = temp[(j + 1) % tn];
            if(vis[p1.id] && vis[p2.id]) res++;
        }
    }

    cout << res + 1 ;
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    int T = 1; 
    while (T--) solve();
    return 0;
}