#include <iostream>
#include <iomanip>
#include <cassert>
#include <algorithm>
#include <functional>
#include <vector>
#include <string>
#include <cstring>
#include <stack>
#include <queue>
#include <map>
#include <bitset>
#include <sstream>
#include <istream>
#include <cmath>
#include <cstdio>

using namespace std;

#define vci vector<int>
#define vcs vector<string>
#define pb push_back
#define sz size()
#define mapii map<int, int>
#define mapci map<char, int>
#define mapsi map<string, int>
#define all(x) x.begin(), x.end()
#define minit(a, i) memset(a, i, sizeof(a));

#define for_(i, a, b) for (int i=(int)a; i<(int)b; i++)
#define for_d(i, a, b) for (int i=(int)a-1; i>=b; i--)
#define for_r(i, a, b, c) for (int i=(int)a; i<(int)b; i += c)
#define for_dr(i, a, b, c) for (int i=(int)a-1; i>=b; i -= c)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)

typedef long long ll;
typedef double D;

const int iINF = 2147483647;
const ll lINF = 9223372036854775807;

template <class T> inline void dbg(T t) { cout << t << endl; }



// define eps
double EPS = 1e-10;

struct Point2D { 
	double x, y;
	Point2D (double a=0, double b=0) : x(a), y(b) {}
};
typedef Point2D Vector2D;

// Point2D's and Vector2D's operator
Point2D operator + (Point2D a, Point2D b) { return Point2D(a.x + b.x, a.y + b.y); }
Point2D operator - (Point2D a, Point2D b) { return Point2D(a.x - b.x, a.y - b.y); }
Point2D operator * (Point2D a, double d) { return Point2D(a.x * d, a.y * d); }
Point2D operator / (Point2D a, double d) { return Point2D(a.x / d, a.y / d); }

bool operator < (const Point2D& a, const Point2D& b) { return a.x != b.x ? a.x < b.x : a.y < b.y; }
bool operator > (const Point2D& a, const Point2D& b) { return b.x != a.x ? b.x < a.x : b.y < a.y; }
bool operator == (const Point2D& a, const Point2D& b) { return fabs(a.x-b.x)<EPS && fabs(a.y-b.y)<EPS; }

double norm(Point2D a) { return a.x*a.x + a.y*a.y; }
double dot2D(const Vector2D& a, const Vector2D& b) { return a.x * b.x + a.y * b.y; }
double cross2D(const Vector2D& a, const Vector2D& b) { return a.x*b.y - a.y*b.x; }

// 点の進行方向	a -> b -> c
int ccw(Point2D a, Point2D b, Point2D c) {
	b = b - a; c = c - a;
	if (cross2D(b, c) > 0) return +1;	// counter clockwise
	if (cross2D(b, c) < 0) return -1;	// clockwise
	if (dot2D(b, c) < 0) return +2;		// c--a--b on line
	if (norm(b) < norm(c)) return -2;	// a--b--c on line
	return 0;	// 
}

vector<Point2D> convexHull(vector<Point2D> ps) {
	int n = (int)ps.size(), k = 0;
	sort(ps.begin(), ps.end());
	vector<Point2D> ch(2*n);	
	for (int i = 0; i < n; ch[k++] = ps[i++]) // lower-hull
		while (k >= 2 && ccw(ch[k-2], ch[k-1], ps[i]) <= 0) --k;
	for (int i = n - 2, t = k + 1; i >= 0; ch[k++] = ps[i--])	// upper-hull
		while (k >= t && ccw(ch[k-2], ch[k-1], ps[i]) <= 0) --k;
	ch.resize(k-1);
	return ch;
}


int main() {
	int n;
	
	while (cin>>n) {
		vector<Point2D> ps(n);
	
		for_(i, 0, n) {
			D x, y;
			scanf("%lf,%lf", &x, &y);
			ps[i].x = x; ps[i].y = y;
		}
	
		vector<Point2D> ch = convexHull(ps);
		int k = (int)ch.sz;
	
		cout << n - k << endl;
	}
	
	return 0;
}