#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
#include <string>
#include <sstream>
#include <stack>
#include <iomanip>
#include <numeric>
#include <queue>
#include <climits>
#include <set>
#include <complex>
#include <cmath>
#include <map>
using namespace std;
using ll = long long;
#define MOD 1000000007
#define INF 1LL << 59

using Point = complex<double>;

istream &operator>>(istream &is, Point &p)
{
    double a, b;
    is >> a >> b;
    p = Point(a, b);
    return is;
}

#define curr(P, i) P[i]
#define next(P, i) P[(i + 1) % P.size()]
#define prev(P, i) P[(i - 1 + P.size()) % P.size()]

const double EPS = 1e-10, PI = acos(-1);
inline bool eq(double a, double b) { return fabs(b - a) < EPS; }

//二つのスカラーが等しいか
#define EQ(a, b) (abs((a) - (b)) < EPS)
//二つのベクトルが等しいか
#define EQV(a, b) (EQ((a), real(), (b).real()) && EQ((a), imag(), (b).imag()))

namespace std
{
bool operator<(const Point &a, const Point &b)
{
    return a.real() != b.real() ? a.real() < b.real() : a.imag() < b.imag();
}
} // namespace std

struct Line
{
    Point a, b;
    Line() {}
    Line(Point a, Point b) : a(a), b(b) {}
    //a, bはそれぞれ座標を指す. これより一つの「line」に対して二個の点を持つことになる
    Line(double A, double B, double C) // Ax + By = C
    {
        if (eq(A, 0))
            a = Point(0, C / B), b = Point(1, C / B);
        else if (eq(B, 0))
            b = Point(C / A, 0), b = Point(C / A, 1);
        else
            a = Point(0, C / B), b = Point(C / A, 0);
    }

    friend ostream &operator<<(ostream &os, Line &p)
    {
        return os << p.a << " to " << p.b;
    }

    friend istream &operator>>(istream &is, Line &a)
    {
        return is >> a.a >> a.b;
    }
};

struct Segment : Line
{
    Segment() {}

    Segment(Point a, Point b) : Line(a, b) {}
};

struct Circle
{
    Point p;
    double r;

    Circle() {}

    Circle(Point p, double r) : p(p), r(r) {}
};

using Points = vector<Point>;
using Polygon = vector<Point>;
using Segments = vector<Segment>;
using Lines = vector<Line>;
using Circles = vector<Circle>;

double dot(const Point a, const Point b)
{
    return real(a) * real(b) + imag(a) * imag(b);
}

double cross(const Point a, const Point b)
{
    return real(a) * imag(b) - imag(a) * real(b);
}
int ccw(const Point &a, Point b, Point c)
{
    b = b - a, c = c - a;
    if (cross(b, c) > EPS)
        return +1; // "COUNTER_CLOCKWISE"
    if (cross(b, c) < -EPS)
        return -1; // "CLOCKWISE"
    if (dot(b, c) < 0)
        return +2; // "ONLINE_BACK"
    if (norm(b) < norm(c))
        return -2; // "ONLINE_FRONT"
    return 0;      // "ON_SEGMENT"
}

enum
{
    OUT,
    ON,
    IN
};

int contains(const Polygon &Q, const Point &p)
{
    bool in = false;
    for (int i = 0; i < Q.size(); ++i)
    {
        Point a = Q[i] - p, b = Q[(i + 1) % Q.size()] - p;
        if (a.imag() > b.imag())
            swap(a, b);
        if (a.imag() <= 0 && 0 < b.imag() && cross(a, b) < 0)
            in = !in;
        if (cross(a, b) == 0 && dot(a, b) <= 0)
            return ON;
    }
    return in ? IN : OUT;
}

Polygon convex_hull(Polygon &p)
{
    int n = (int)p.size(), k = 0;
    if (n <= 2)
        return p;
    sort(p.begin(), p.end());
    vector<Point> ch(n * 2);

    for (int i = 0; i < n; ch[k++] = p[i++])
    {
        while (k >= 2 && cross(ch[k - 1] - ch[k - 2], p[i] - ch[k - 1]) < 0)
            --k;
    }

    for (int i = n - 2, t = k + 1; i >= 0; ch[k++] = p[i--])
    {
        while (k >= t && cross(ch[k - 1] - ch[k - 2], p[i] - ch[k - 1]) < 0)
            --k;
    }
    ch.resize(k - 1);
    return ch;
}
int main()
{
    //std::ios::sync_with_stdio(false);
    //std::cin.tie(0);
    //cout << fixed << setprecision(7);

    int n;
    while (cin >> n)
    {
        if (n == 0)
            break;

        Polygon Q;
        for (int i = 0; i < n; ++i)
        {
            double px, py;
            scanf("%lf,%lf", &px, &py);
            Point p(px, py);
            Q.push_back(p);
        }

        Polygon P = convex_hull(Q);
        cout << n - P.size() << endl;
    }

    return 0;
}


Measured memory_bytes: 3204