#include <iostream>
#include <algorithm>
#include <vector>
#include <sstream>
#include <string>
#include <cmath>

using namespace std;

const double EPS=1e-9;

namespace FP {
    bool isZero(double x) {
        return (abs(x) <= EPS);
    }
};

struct Point {
    double x, y;
    Point(double x=0, double y=0) : x(x), y(y) {}
    Point(const Point &o) : x(o.x), y(o.y) {}
    string to_s() {
        ostringstream os;
        os << "(" << x << "," << y << ")";
        return os.str();
    }
    bool operator<(const Point &o) const {
        return x == o.x ? y < o.y : x < o.x;
    }
    bool operator==(const Point &o) const {
        return x == o.x && y == o.y;
    }
    Point operator+(const Point &o) const {
        return Point(x+o.x, y+o.y);
    }
    Point operator-(const Point &o) const {
        return Point(x-o.x, y-o.y);
    }
    Point operator*(const double m) const {
        return Point(x*m, y*m);
    }
    Point operator/(const double d) const {
        return Point(x/d, y/d);
    }
    // 外積
    double cross(const Point &o) const {
        return x * o.y - y * o.x;
    }
    // 内積
    double dot(const Point &o) const {
        return x * o.x + y * o.y;
    }
    // ベクトルがx軸となす角
    double atan() const {
        return atan2(y, x);
    }
    // ベクトルの長さの二乗
    double norm() const {
        return dot(*this);
    }
};

struct Line {
    double a, b, c;
    Line(double a=0, double b=0, double c=0) :
        a(a), b(b), c(c) {}
    Point intersectionPoint(const Line &l) const {
        double d = a * l.b - l.a * b;
        if (!intersects(l)) {
            throw string("The 2 Lines are parallel");
        }
        double x = (b * l.c - l.b * c) / d;
        double y = (l.a * c - a * l.c) / d;
        return Point(x, y);
    }
    bool intersects(const Line &l) const {
        return !FP::isZero(a * l.b - l.a * b);
    }
    string to_s() {
        ostringstream os;
        os << a << ' ' << b << ' ' << c;
        return os.str();
    }
    static Line fromPoints(const Point &a, const Point &b) {
        double dx = b.x - a.x;
        double dy = b.y - a.y;
        return Line(dy, -dx, dx * a.y - dy * a.x);
    }
    static Line fromPoints(double x1, double y1, double x2, double y2) {
        return fromPoints(Point(x1, y1), Point(x2, y2));
    }
};

struct LineSegment {
    Point start, end;
    LineSegment(const Point &start, const Point &end) : start(start), end(end) {}
    LineSegment(double x1, double y1, double x2, double y2) : start(Point(x1, y1)), end(Point(x2, y2)) {}
    string to_s() {
        ostringstream os;
        os << '(' << start.x << ',' << start.y << ')' << '-' << '(' << end.x << ',' << end.y << ')' << endl;
        return os.str();
    }
    Line toLine() const {
        return Line::fromPoints(start, end);
    }
    bool intersects(const Line &l) const {
        double t1 = l.a * start.x + l.b * start.y + l.c;
        double t2 = l.a * end.x + l.b * end.y + l.c;
        return t1 * t2 <= 0;
    }
    bool intersects(const LineSegment &s) const {
        return intersects(s.toLine()) && s.intersects(toLine());
    }
    Line perpendicularBisector() const {
        Point p1 = (start + end) / 2;
        Point p2;
        p2.x = -(end - p1).y;
        p2.y = (end - p1).x;
        p2 = p2 + p1;
        return Line::fromPoints(p1, p2);
    }
};

struct Polygon {
    vector<Point> vertex;
    Polygon(){}
    Polygon(vector<Point> vertex) : vertex(vertex) {}
    void addVertex(Point v) {
        vertex.push_back(v);
    }
    Point next(int v) const {
        return vertex[(v+1) % vertex.size()];
    }
    Point prev(int v) const {
        return vertex[(v-1+vertex.size()) % vertex.size()];
    }
    int size() const {
        return vertex.size();
    }
    const double area() const {
        double ret = 0;
        for (int i = 0; i < vertex.size(); i++) {
            ret += vertex[i].cross(next(i));
        }
        return abs(ret)*0.5;
    }
};

const int CCW = 1;
const int CW  = -1;
const int ON_SAME_LINE = 0;
int ccw(Point a, Point b, Point c) {
    b = b-a; c = c-a;
    if (b.cross(c) > EPS) return +1;
    if (b.cross(c) < -EPS) return -1;
    return 0;
}

vector<Point> convexHull(vector<Point> ps) {
    int n = ps.size();
    sort(ps.begin(), ps.end());

    vector<Point> upper;
    upper.push_back(ps[0]);
    upper.push_back(ps[1]);

    for (int i = 2; i < n; i++) {
        upper.push_back(ps[i]);
        int j = upper.size();
        while (j > 2 && ccw(upper[j-3], upper[j-2], upper[j-1]) == CCW) {
            upper.erase(upper.begin()+j-2);
            j = upper.size();
        }
    }

    vector<Point> lower;
    lower.push_back(ps[n-1]);
    lower.push_back(ps[n-2]);
    
    for (int i = n-3; i >= 0; i--) {
        lower.push_back(ps[i]);
        int j = lower.size();
        while (j > 2 && ccw(lower[j-3], lower[j-2], lower[j-1]) == CCW) {
            lower.erase(lower.begin()+j-2);
            j = lower.size();
        }
    }

    vector<Point> hull;
    for (int i = 0; i < upper.size(); i++) hull.push_back(upper[i]);
    for (int i = 0; i < lower.size(); i++) hull.push_back(lower[i]);
    sort(hull.begin(), hull.end());
    hull.erase(unique(hull.begin(), hull.end()), hull.end());
    return hull;
}

int main() {
    int n;
    while (cin >> n) {
        if (n == 0) break;
        vector<Point> ps;
        for (int i = 0; i < n; i++) {
            char d; double x, y; cin >> x >> d >> y;
            ps.push_back(Point(x, y));
        }
        cout << ps.size() - convexHull(ps).size() << endl;
    }
    return 0;
}